Hookah device

ABSTRACT

A hookah device ( 202 ) which attaches to a hookah ( 246 ). The hookah device ( 202 ) comprises a plurality of ultrasonic mist generator devices ( 201 ) for generating a mist for inhalation by a user. The hookah device ( 202 ) comprises a driver device ( 202 ) which controls the mist generator devices ( 201 ) to maximize the efficiency of mist generation by the mist generator devices ( 201 ) and optimize mist output from the hookah device ( 202 ).

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.17/300,931, filed Dec. 15, 2021, which claims the benefit of priority toand incorporates by reference herein the entirety of all the followingapplications:

U.S. application Ser. No. 17/223,846 filed on 6 Apr. 2021 (the '846application), which claims the benefit of priority to and incorporatesby reference herein the entirety of each of: European patent applicationno. 20168245.7, filed on 6 Apr. 2020; European patent application no.20168231.7, filed on 6 Apr. 2020; and European patent application no.20168938.7, filed on 9 Apr. 2020; the '846 application is a continuationin part of U.S. application Ser. No. 16/889,667, filed on 1 Jun. 2020;the '846 application is also a continuation in part of U.S. applicationSer. No. 17/065,992, filed on 8 Oct. 2020, which itself is acontinuation in part of U.S. application Ser. No. 16/889,667, filed on 1Jun. 2020 and claims the benefit of priority to U.S. provisional patentapplication No. 63/064,386, filed on 11 Aug. 2020; the '846 applicationis also a continuation in part of U.S. patent application Ser. No.17/122,025, filed on 15 Dec. 2020 which itself claims the benefit ofpriority to International patent application nos. PCT/IB2019/060808,PCT/IB2019/060810, PCT/IB2019/060811, and PCT/IB2019/060812, all filedon 15 Dec. 2019; and the '846 application is also a continuation in partof U.S. application Ser. No. 17/220,189, filed on 1 Apr. 2021;

U.S. application Ser. No. 17/122,025 filed on 15 Dec. 2020 which claimsthe benefit of priority to International patent application no.PCT/IB2019/060808, filed on 15 Dec. 2019, International patentapplication no. PCT/IB2019/060810, filed on 15 Dec. 2019, Internationalpatent application no. PCT/IB2019/060811, filed on 15 Dec. 2019,International patent application no. PCT/IB2019/060812, filed on 15 Dec.2019, European patent application no. 20168245.7, filed on 6 Apr. 2020,European patent application no. 20168231.7, filed on 6 Apr. 2020, andEuropean patent application no. 20168938.7, filed on 9 Apr. 2020;

U.S. application Ser. No. 17/220,189 filed on 1 Apr. 2021 which claimsthe benefit of priority to European Patent Application No. 20168231.7,filed on 6 Apr. 2020; and

UK patent application no. 2104872.3, filed 6 Apr. 2021, all of theforegoing applications are incorporated herein by reference in theirentirety.

FIELD

The present invention relates to a hookah device. The present inventionmore particularly relates to a hookah device which generates a mistusing ultrasonic vibrations.

BACKGROUND

The traditional hookah is a smoking device which burns tobacco leavesthat have been crushed and prepared specifically to be heated usingcharcoal. The heat from the charcoal causes the crushed tobacco leavesto burn, producing smoke that is pulled through water in a glass chamberand to the user by inhalation. The water is used to cool the hot smokefor ease of inhalation.

Hookah use began centuries ago in ancient Persia and India. Today,hookah cafés are gaining popularity around the world, including theUnited Kingdom, France, Russia, the Middle East and the United States.

A typical modern hookah has a head (with holes in the bottom), a metalbody, a water bowl and a flexible hose with a mouthpiece. New forms ofelectronic hookah products, including steam stones and hookah pens, havebeen introduced. These products are battery or mains powered and heatliquid containing nicotine, flavorings and other chemicals to producesmoke which is inhaled.

Although many users consider it less harmful than smoking cigarettes,hookah smoking has many of the same health risks as cigarette smoking.

Thus, a need exists in the art for an improved hookah device which seeksto address at least some of the problems described herein.

The present invention seeks to provide an improved hookah device.

SUMMARY

The present invention provides a hookah device as claimed in claim 1 anda hookah as claimed in claim 19. The present invention also providespreferred embodiments as claimed in the dependent claims.

The various examples of this disclosure which are described below havemultiple benefits and advantages over conventional hookah devices andhookahs. These benefits and advantages are set out in the descriptionbelow.

The hookah device of examples of this disclosure has an environmentalbenefit since the hookah device does not emit any smoke and hookahdevice removes the need to burn charcoal.

According to some arrangements, there is provided a hookah devicecomprising: a plurality of ultrasonic mist generator devices which areeach provided with a respective mist outlet port; a driver device whichis connected electrically to each of the mist generator devices andconfigured to activate the mist generator devices; and a hookahattachment arrangement which is configured to attach the hookah deviceto a hookah, the hookah attachment arrangement having a hookah outletport which provides a fluid flow path from the mist outlet ports of themist generator devices and out of the hookah device such that, when atleast one of the mist generator devices is activated by the driverdevice, mist generated by each activated mist generator device flowsalong the fluid flow path and out of the hookah device to the hookah.

In some arrangements, the driver device is connected electrically toeach of the mist generator devices by a data bus and the driver deviceis configured to identify and control each mist generator device using arespective unique identifier for the mist generator device.

In some arrangements, each mist generator device comprises: anidentification arrangement comprising: an integrated circuit having amemory which stores a unique identifier for the mist generator device;and an electrical connection which provides an electronic interface forcommunication with the integrated circuit.

In some arrangements, the driver device is configured to control eachrespective mist generator device to activate independently of the othermist generator devices.

In some arrangements, the driver device is configured to control themist generator devices to activate in a predetermined sequence.

In some arrangements, each mist generator device comprises: a manifoldhaving a manifold pipe which is in fluid communication with the mistoutlet ports of the mist generator devices, wherein mist output from themist outlet ports combines in the manifold pipe and flows through themanifold pipe and out from the hookah device.

In some arrangements, the hookah device comprises four mist generatordevices which are releasably coupled to the manifold at 90° relative toone another.

In some arrangements, each mist generator device is releasably attachedto the driver device so that each mist generator device is separablefrom the driver device.

In some arrangements, each mist generator device comprises: a mistgenerator housing which is elongate and comprises an air inlet port andthe said mist outlet port; a liquid chamber provided within the mistgenerator housing, the liquid chamber containing a liquid to beatomized; a sonication chamber provided within the mist generatorhousing; a capillary element extending between the liquid chamber andthe sonication chamber such that a first portion of the capillaryelement is within the liquid chamber and a second portion of thecapillary element is within the sonication chamber; an ultrasonictransducer having a generally planar atomization surface which isprovided within the sonication chamber, the ultrasonic transducer beingmounted within the mist generator housing such that the plane of theatomization surface is substantially parallel with a longitudinal lengthof the mist generator housing, wherein part of the second portion of thecapillary element is superimposed on part of the atomization surface,and wherein the ultrasonic transducer is configured to vibrate theatomization surface to atomize a liquid carried by the second portion ofthe capillary element to generate a mist comprising the atomized liquidand air within the sonication chamber; and an airflow arrangement whichprovides an air flow path between the air inlet port, the sonicationchamber and the air outlet port.

In some arrangements, each mist generator device further comprises: atransducer holder which is held within the mist generator housing,wherein the transducer element holds the ultrasonic transducer andretains the second portion of the capillary element superimposed on partof the atomization surface; and a divider portion which provides abarrier between the liquid chamber and the sonication chamber, whereinthe divider portion comprises a capillary aperture through which part ofthe first portion of the capillary element extends.

In some arrangements, the capillary element is 100% bamboo fiber.

In some arrangements, the airflow arrangement is configured to changethe direction of a flow of air along the air flow path such that theflow of air is substantially perpendicular to the atomization surface ofthe ultrasonic transducer as the flow of air passes into the sonicationchamber.

In some arrangements, the liquid chamber contains a liquid having akinematic viscosity between 1.05 Pa·s and 1.412 Pa·s and a liquiddensity between 1.1 g/ml and 1.3 g/ml.

In some arrangements, the liquid chamber contains a liquid comprisingapproximately a 2:1 molar ratio of levulinic acid to nicotine.

In some arrangements, the driver device comprises: an AC driver which isconfigured to generate an AC drive signal at a predetermined frequencyto drive a respective ultrasonic transducer in each mist generatordevice; an active power monitoring arrangement which is configured tomonitor the active power used by the ultrasonic transducer when theultrasonic transducer is driven by the AC drive signal, wherein theactive power monitoring arrangement is configured to provide amonitoring signal which is indicative of an active power used by theultrasonic transducer; a processor which is configured to control the ACdriver and to receive the monitoring signal drive from the active powermonitoring arrangement; and a memory storing instructions which, whenexecuted by the processor, cause the processor to:

-   -   A. control the AC driver to output an AC drive signal to the        ultrasonic transducer at a predetermined sweep frequency;    -   B. calculate the active power being used by the ultrasonic        transducer based on the monitoring signal;    -   C. control the AC driver to modulate the AC drive signal to        maximize the active power being used by the ultrasonic        transducer;    -   D. store a record in the memory of the maximum active power used        by the ultrasonic transducer and the sweep frequency of the AC        drive signal;    -   E. repeat steps A-D for a predetermined number of iterations        with the sweep frequency incrementing with each iteration such        that, after the predetermined number of iterations has occurred,        the sweep frequency has been incremented from a start sweep        frequency to an end sweep frequency;    -   F. identify from the records stored in the memory the optimum        frequency for the AC drive signal which is the sweep frequency        of the AC drive signal at which a maximum active power is used        by the ultrasonic transducer; and    -   G. control the AC driver to output an AC drive signal to the        ultrasonic transducer at the optimum frequency to drive the        ultrasonic transducer to atomize a liquid.

In some arrangements, the active power monitoring arrangement comprises:a current sensing arrangement which is configured to sense a drivecurrent of the AC drive signal driving the ultrasonic transducer,wherein the active power monitoring arrangement is configured to providea monitoring signal which is indicative of the sensed drive current.

In some arrangements, the memory stores instructions which, whenexecuted by the processor, cause the processor to: repeat steps A-D withthe sweep frequency being incremented from a start sweep frequency of2900 kHz to an end sweep frequency of 2960 kHz.

In some arrangements, the memory stores instructions which, whenexecuted by the processor, cause the processor to: repeat steps A-D withthe sweep frequency being incremented from a start sweep frequency of2900 kHz to an end sweep frequency of 3100 kHz.

In some arrangements, the AC driver is configured to modulate the ACdrive signal by pulse width modulation to maximize the active powerbeing used by the ultrasonic transducer.

According to some arrangements, there is provided a hookah comprising: awater chamber; an elongate stem having a first end which is attached tothe water chamber, the stem comprising a mist flow path which extendsfrom a second end of the stem, through the stem, to the first end; and ahookah device according to any one of claims 1 to 19 as definedhereinafter, wherein the hookah attachment arrangement of the hookahdevice is attached to the stem of the hookah at the second end of thestem.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the present invention may be more readily understood,embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is an exploded view of components of an ultrasonic mist inhaler.

FIG. 2 is an exploded view of components of an inhaler liquid reservoirstructure.

FIG. 3 is a cross section view of components of an inhaler liquidreservoir structure.

FIG. 4A is an isometric view of an airflow member of the inhaler liquidreservoir structure according to FIGS. 2 and 3.

FIG. 4B is a cross section view of the airflow member shown in FIG. 4A.

FIG. 5 is schematic diagram showing a piezoelectric transducer modelledas an RLC circuit.

FIG. 6 is graph of frequency versus log impedance of an RLC circuit.

FIG. 7 is graph of frequency versus log impedance showing inductive andcapacitive regions of operation of a piezoelectric transducer.

FIG. 8 is flow diagram showing the operation of a frequency controller.

FIG. 9 is a diagrammatic perspective view of a mist generator device ofthis disclosure.

FIG. 10 is a diagrammatic perspective view of a mist generator device ofthis disclosure.

FIG. 11 is a diagrammatic exploded perspective view of a mist generatordevice of this disclosure.

FIG. 12 is a diagrammatic perspective view of a transducer holder ofthis disclosure.

FIG. 13 is a diagrammatic perspective view of a transducer holder ofthis disclosure.

FIG. 14 is a diagrammatic perspective view of a capillary element ofthis disclosure.

FIG. 15 is a diagrammatic perspective view of a capillary element ofthis disclosure.

FIG. 16 is a diagrammatic perspective view of a transducer holder ofthis disclosure.

FIG. 17 is a diagrammatic perspective view of a transducer holder ofthis disclosure.

FIG. 18 is a diagrammatic perspective view of a part of a housing ofthis disclosure.

FIG. 19 is a diagrammatic perspective view of an absorbent element ofthis disclosure.

FIG. 20 is a diagrammatic perspective view of a part of a housing ofthis disclosure.

FIG. 21 is a diagrammatic perspective view of a part of a housing ofthis disclosure.

FIG. 22 is a diagrammatic perspective view of an absorbent element ofthis disclosure.

FIG. 23 is a diagrammatic perspective view of a part of a housing ofthis disclosure.

FIG. 24 is a diagrammatic perspective view of a part of a housing ofthis disclosure.

FIG. 25 is a diagrammatic perspective view of a part of a housing ofthis disclosure.

FIG. 26 is a diagrammatic perspective view of a circuit board of thisdisclosure.

FIG. 27 is a diagrammatic perspective view of a circuit board of thisdisclosure.

FIG. 28 is a diagrammatic exploded perspective view of a mist generatordevice of this disclosure.

FIG. 29 is a diagrammatic exploded perspective view of a mist generatordevice of this disclosure.

FIG. 30 is a schematic diagram of an integrated circuit arrangement ofthis disclosure.

FIG. 31 is a schematic diagram of an integrated circuit of thisdisclosure.

FIG. 32 is a schematic diagram of a pulse width modulation generator ofthis disclosure.

FIG. 33 is timing diagram of an example of this disclosure.

FIG. 34 is timing diagram of an example of this disclosure.

FIG. 35 is a table showing port functions of an example of thisdisclosure.

FIG. 36 is a schematic diagram of an integrated circuit of thisdisclosure.

FIG. 37 is a circuit diagram of an H-bridge of an example of thisdisclosure.

FIG. 38 is a circuit diagram of a current sense arrangement of anexample of this disclosure.

FIG. 39 is a circuit diagram of an H-bridge of an example of thisdisclosure.

FIG. 40 is a graph showing the voltages during the phases of operationof the H-bridge of FIG. 37.

FIG. 41 is a graph showing the voltages during the phases of operationof the H-bridge of FIG. 37.

FIG. 42 is a graph showing the voltage and current at a terminal of anultrasonic transducer while the ultrasonic transducer is being driven bythe H-bridge of FIG. 37.

FIG. 43 is a schematic diagram showing connections between integratedcircuits of this disclosure.

FIG. 44 is a schematic diagram of an integrated circuit of thisdisclosure.

FIG. 45 is diagram illustrating the steps of an authentication method ofan example of this disclosure.

FIG. 46 is a cross sectional view of a mist generator device of thisdisclosure.

FIG. 47 is a cross sectional view of a mist generator device of thisdisclosure.

FIG. 48 is a cross sectional view of a mist generator device of thisdisclosure.

FIG. 49 is a diagrammatic perspective view of a hookah device of thisdisclosure.

FIG. 50 is a diagrammatic perspective view of a hookah device of thisdisclosure attached to a hookah body and water bowl of a hookahapparatus.

FIG. 51 is a diagrammatic exploded perspective view of a hookah deviceof this disclosure.

FIG. 52 is a diagrammatic perspective view of components of a hookahdevice of this disclosure.

FIG. 53 is a diagrammatic perspective view of components of a hookahdevice of this disclosure.

FIG. 54 is a diagrammatic perspective view of a component of a hookahdevice of this disclosure.

FIG. 55 is a diagrammatic perspective view of a component of a hookahdevice of this disclosure.

FIG. 56 is a diagrammatic perspective view of a component of a hookahdevice and four mist generator devices of this disclosure.

FIG. 57 is a diagrammatic perspective view of components of a hookahdevice of this disclosure.

FIG. 58 is a diagrammatic cross-sectional view of components of a hookahdevice of this disclosure.

FIG. 59 is a diagrammatic perspective view of a hookah device of thisdisclosure attached to a hookah body and water bowl of a hookahapparatus.

DETAILED DESCRIPTION

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components, concentrations, applicationsand arrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, the attachment of a first feature and a secondfeature in the description that follows may include embodiments in whichthe first feature and the second feature are attached in direct contact,and may also include embodiments in which additional features may bepositioned between the first feature and the second feature, such thatthe first feature and the second feature may not be in direct contact.In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

The following disclosure describes representative arrangements orexamples. Each arrangement or example may be considered to be anembodiment and any reference to an “arrangement” or an “example” may bechanged to “embodiment” in the present disclosure.

A hookah device of some arrangements incorporates ultrasonicaerosolization technology. The hookah device of some arrangements isconfigured to replace a conventional hookah head (coal-heated orelectronically heated). The hookah device of some arrangementsreleasably attaches to an existing stem or metal body and waterchamber/bowl in place of the conventional hookah head which houses thetobacco and the charcoal (or electronic heating element).

In other arrangements, the hookah device is provided with a stem/bodyand a water chamber/bowl as a complete hookah apparatus.

Hookah water bowls come in various shapes and sizes, ornamented withtraditional or futuristic decorations as per individual preferences. Thedesign and development of the ultrasonic aerosolizing hookah device ofsome arrangements was executed, keeping the tradition in mind, to createa replaceable head that fits onto any existing hookah.

The following disclosure describes the components and functionality ofan ultrasonic mist generator device. The disclosure then describes thehookah device of some arrangements which incorporates a plurality ofultrasonic mist generator devices.

Conventional electronic vaporizing inhalers tend to rely on inducinghigh temperatures of a metal component configured to heat a liquid inthe inhaler, thus vaporizing the liquid that can be breathed in. Theliquid typically contains nicotine and flavorings blended into asolution of propylene glycol (PG) and vegetable glycerin (VG), which isvaporized via a heating component at high temperatures. Problems withconventional inhalers may include the possibility of burning metal andsubsequent breathing in of the metal along with the burnt liquid. Inaddition, some may not prefer the burnt smell or taste caused by theheated liquid.

FIGS. 1 to 4 illustrate an ultrasonic mist inhaler comprising asonication chamber. It is noted that the expression “mist” used in thefollowing disclosure means the liquid is not heated as usually intraditional inhalers known from the prior art. In fact, traditionalinhalers use heating elements to heat the liquid above its boilingtemperature to produce a vapor, which is different from a mist.

When sonicating liquids at high intensities, the sound waves thatpropagate into the liquid media result in alternating high-pressure(compression) and low-pressure (rarefaction) cycles, at different ratesdepending on the frequency. During the low-pressure cycle,high-intensity ultrasonic waves create small vacuum bubbles or voids inthe liquid. This phenomenon is termed cavitation. When the bubblesattain a volume at which they can no longer absorb energy, they collapseviolently during a high-pressure cycle. During the implosion, very highpressures are reached locally. At cavitation, broken capillary waves aregenerated, and tiny droplets break the surface tension of the liquid andare quickly released into the air, taking mist form.

The following will explain more precisely the cavitation phenomenon.

When the liquid is atomized by ultrasonic vibrations, micro waterbubbles are produced in the liquid.

The bubble production is a process of formation of cavities created bythe negative pressure generated by intense ultrasonic waves generated bythe means of ultrasonic vibrations.

High intensity ultrasonic sound waves leading to rapid growth ofcavities with relatively low and negligible reduction in cavity sizeduring the positive pressure cycle.

Ultrasound waves, like all sound waves, consist of cycles of compressionand expansion. When in contact with a liquid, Compression cycles exert apositive pressure on the liquid, pushing the molecules together.Expansion cycles exert a negative pressure, pulling the molecules awayfrom another.

Intense ultrasound waves create regions of positive pressure andnegative pressure. A cavity can form and grow during the episodes ofnegative pressure. When the cavity attains a critical size, the cavityimplodes.

The amount of negative pressure needed depends on the type and purity ofthe liquid. For truly pure liquids, tensile strengths are so great thatavailable ultrasound generators cannot produce enough negative pressureto make cavities. In pure water, for instance, more than 1,000atmospheres of negative pressure would be required, yet the mostpowerful ultrasound generators produce only about 50 atmospheres ofnegative pressure. The tensile strength of liquids is reduced by the gastrapped within the crevices of the liquid particles. The effect isanalogous to the reduction in strength that occurs from cracks in solidmaterials. When a crevice filled with gas is exposed to anegative-pressure cycle from a sound wave, the reduced pressure makesthe gas in the crevice expand until a small bubble is released intosolution.

However, a bubble irradiated with ultrasound continually absorbs energyfrom alternating compression and expansion cycles of the sound wave.These cause the bubbles to grow and contract, striking a dynamic balancebetween the void inside the bubble and the liquid outside. In somecases, ultrasonic waves will sustain a bubble that simply oscillates insize. In other cases, the average size of the bubble will increase.

Cavity growth depends on the intensity of sound. High-intensityultrasound can expand the cavity so rapidly during the negative-pressurecycle that the cavity never has a chance to shrink during thepositive-pressure cycle. In this process, cavities can grow rapidly inthe course of a single cycle of sound.

For low-intensity ultrasound the size of the cavity oscillates in phasewith the expansion and compression cycles. The surface of a cavityproduced by low-intensity ultrasound is slightly greater duringexpansion cycles than during compression cycles. Since the amount of gasthat diffuses in or out of the cavity depends on the surface area,diffusion into the cavity during expansion cycles will be slightlygreater than diffusion out during compression cycles. For each cycle ofsound, then, the cavity expands a little more than it shrinks. Over manycycles the cavities will grow slowly.

It has been noticed that the growing cavity can eventually reach acritical size where it will most efficiently absorb energy from theultrasound. The critical size depends on the frequency of the ultrasoundwave. Once a cavity has experienced a very rapid growth caused by highintensity ultrasound, it can no longer absorb energy as efficiently fromthe sound waves. Without this energy input the cavity can no longersustain itself. The liquid rushes in and the cavity implodes due to anon-linear response.

The energy released from the implosion causes the liquid to befragmented into microscopic particles which are dispersed into the airas mist.

The equation for description of the above non-linear response phenomenonmay be described by the “Rayleigh-Plesset” equation. This equation canbe derived from the “Navier-Stokes” equation used in fluid dynamics.

The inventors approach was to rewrite the “Rayleigh-Plesset” equation inwhich the bubble volume, V, is used as the dynamic parameter and wherethe physics describing the dissipation is identical to that used in themore classical form where the radius is the dynamic parameter.

The equation used derived as follows:

${\left. \frac{❘{\frac{1}{c^{2}}\frac{\delta^{2}\phi}{\delta t^{2}}}❘}{\nabla^{2}\phi} \right.\sim\left( \frac{R}{\lambda} \right)} \ll 1$${\frac{1}{4\pi}\left( \frac{4\pi}{3V} \right)^{\frac{1}{3}}\left( {\overset{¨}{V} - \frac{{\overset{.}{V}}^{2}(t)}{6V}} \right)} = {\frac{1}{\rho_{0}}\left( {{\left( {p_{0} + {2{\sigma\left( \frac{4\pi}{3V_{0}} \right)}^{\frac{1}{3}}} - p_{V}} \right)\left( \frac{V_{0}}{V} \right)^{\kappa}} + p_{V} - {2{\sigma\left( \frac{4\pi}{3V} \right)}^{\frac{1}{3}}} - p_{0} - {P(t)}} \right)}$

wherein:

V is the bubble volume

V₀ is the equilibrium bubble volume

ρ₀ is the liquid density (assumed to be constant)

σ is the surface tension

p_(V) is the vapor pressure

p₀ is the static pressure in the liquid just outside the bubble wall

κ is the polytropic index of the gas

t is the time

R(t) is the bubble radius

P(t) is the applied pressure

c is the speed sound of the liquid

ϕ is the velocity potential

λ is the wavelength of the insonifying field

In the ultrasonic mist inhaler, the liquid has a kinematic viscositybetween 1.05 Pa·sec and 1.412 Pa·sec.

By solving the above equation with the right parameters of viscosity,density and having a desired target bubble volume of liquid spray intothe air, it has been found that the frequency range of 2.8 MHz to 3.2MHz for liquid viscosity range of 1.05 Pa·s and 1.412 Pa·s produce abubble volume of about 0.25 to 0.5 microns.

The process of ultrasonic cavitation has a significant impact on thenicotine concentration in the produced mist.

No heating elements are involved, thereby leading to no burnt elementsand reducing second-hand smoke effects.

In some arrangements, said liquid comprises 57-70% (w/w) vegetableglycerin and 30-43% (w/w) propylene glycol, said propylene glycolincluding nicotine and optionally flavorings.

In the ultrasonic mist inhaler, a capillary element may extend betweenthe sonication chamber and the liquid chamber.

In the ultrasonic mist inhaler, the capillary element is a material atleast partly in bamboo fibers.

The capillary element allows a high absorption capacity, a high rate ofabsorption as well as a high fluid-retention ratio.

It was found that the inherent properties of the proposed material usedfor the capillarity have a significant impact on the efficientfunctioning of the ultrasonic mist inhaler.

Further, inherent properties of the proposed material include a goodhygroscopicity while maintaining a good permeability. This allows thedrawn liquid to efficiently permeate the capillary while the observedhigh absorption capacity allows the retention of a considerable amountof liquid thus allowing the ultrasonic mist inhaler to last for a longertime when compared with the other products available in the market.

Another significant advantage of using the bamboo fibers is thenaturally occurring antimicrobial bio-agent namely “Kun” inherentlypresent within the bamboo fiber making it antibacterial, anti-fungal andodor resistant, making it suitable for medical applications.

The inherent properties have been verified using numerical analysisregarding the benefits of the bamboo fiber for sonication.

The following formulae have been tested with bamboo fibers material andothers material such cotton, paper, or other fiber strands for the useas capillary element and demonstrates that bamboo fibers have muchbetter properties for the use in sonication:

$C = {A + \frac{T}{W_{f}} - \frac{1}{P_{f}} + {\left( {1 - \alpha} \right)\frac{V_{d}}{W_{f}}}}$

wherein:

C (cc/gm of fluid/gm) is the volume per mass of the liquid absorbeddivided by the dry mass of the capillary element,

A (cm²) is the total surface area of the capillary element

T (cm) is the thickness of the capillary element,

W_(f) (gm) is the mass of the dry capillary element,

P_(f) (cc/g·sec) is the density of the dry capillary element,

α is the ratio of increase in volume of capillary element upon wettingto the volume of liquid diffused in the capillary element,

V_(d) (cc) is the amount of liquid diffused in the capillary element

${{Absorbent}{Rate}},{Q = {\frac{\pi r{\gamma 1cos\theta}}{2\eta} \cdot \left( {\frac{T}{W_{f}} - \frac{1}{{AP}_{f}}} \right)}}$

Q (cc/sec) is the amount of liquid absorbed per unit time,

r (cm) is the radius of the pores within the capillary element,

γ (N/m) is the surface tension of the liquid,

θ (degrees) is the angle of contact of the fiber,

η (m²/sec) is the viscosity of the fluid.

FIG. 1 depicts a disposable ultrasonic mist inhaler 100. As can be seenin FIG. 1, the ultrasonic mist inhaler 100 has a cylindrical body with arelatively long length as compared to the diameter. In terms of shapeand appearance, the ultrasonic mist inhaler 100 is designed to mimic thelook of a typical cigarette. For instance, the inhaler can feature afirst portion 101 that primarily simulates the tobacco rod portion of acigarette and a second portion 102 that primarily simulates a filter. Inthe disposable arrangement, the first portion and second portion areregions of a single, but-separable device. The designation of a firstportion 101 and a second portion 102 is used to convenientlydifferentiate the components that are primarily contained in eachportion.

As can be seen in FIG. 1, the ultrasonic mist inhaler comprises amouthpiece 1, a liquid reservoir structure 2 and a casing 3. The firstportion 101 comprises the casing 3 and the second portion 102 comprisesthe mouthpiece 1 and the reservoir structure 2.

The first portion 101 contains the power supply energy.

An electrical storage device 30 powers the ultrasonic mist inhaler 100.The electrical storage device 30 can be a battery, including but notlimited to a lithium-ion, alkaline, zinc-carbon, nickel-metal hydride,or nickel-cadmium battery; a super capacitor; or a combination thereof.In the disposable arrangement, the electrical storage device 30 is notrechargeable, but, in the reusable arrangement, the electrical storagedevice 30 would be selected for its ability to recharge. In thedisposable arrangement, the electrical storage device 30 is primarilyselected to deliver a constant voltage over the life of the inhaler 100.Otherwise, the performance of the inhaler would degrade over time.Preferred electrical storage devices that are able to provide aconsistent voltage output over the life of the device includelithium-ion and lithium polymer batteries.

The electrical storage device 30 has a first end 30 a that generallycorresponds to a positive terminal and a second end 30 b that generallycorresponds to a negative terminal. The negative terminal is extendingto the first end 30 a.

Because the electrical storage device 30 is located in the first portion101 and the liquid reservoir structure 2 is located in the secondportion 102, the joint needs to provide electrical communication betweenthose components. Electrical communication is established using at leastan electrode or probe that is compressed together when the first portion101 is tightened into the second portion 102.

In order for the device to be reusable, the electrical storage device 30is rechargeable. The casing 3 contains a charging port 32.

The integrated circuit 4 has a proximal end 4 a and a distal end 4 b.The positive terminal at the first end 30 a of the electrical storagedevice 30 is in electrical communication with a positive lead of theflexible integrated circuit 4. The negative terminal at the second end30 b of the electrical storage device 30 is in electrical communicationwith a negative lead of the integrated circuit 4. The distal end 4 b ofthe integrated circuit 4 comprises a microprocessor. The microprocessoris configured to process data from a sensor, to control a light, todirect current flow to means of ultrasonic vibrations 5 in the secondportion 102, and to terminate current flow after a pre-programmed amountof time.

The sensor detects when the ultrasonic mist inhaler 100 is in use (whenthe user draws on the inhaler) and activates the microprocessor. Thesensor can be selected to detect changes in pressure, air flow, orvibration. In one arrangement, the sensor is a pressure sensor. In thedigital device, the sensor takes continuous readings which in turnrequires the digital sensor to continuously draw current, but the amountis small and overall battery life would be negligibly affected.

In some arrangements, the integrated circuit 4 comprises a H bridge,which may be formed by 4 MOSFETs to convert a direct current into analternate current at high frequency.

Referring to FIG. 2 and FIG. 3, illustrations of a liquid reservoirstructure 2 according to an arrangement are shown. The liquid reservoirstructure 2 comprises a liquid chamber 21 adapted to receive liquid tobe atomized and a sonication chamber 22 in fluid communication with theliquid chamber 21.

In the arrangement shown, the liquid reservoir structure 2 comprises aninhalation channel 20 providing an air passage from the sonicationchamber 22 toward the surroundings.

As an arrangement of sensor position, the sensor may be located in thesonication chamber 22.

The inhalation channel 20 has a frustoconical element 20 a and an innercontainer 20 b.

As depicted in FIGS. 4A and 46, further the inhalation channel 20 has anairflow member 27 for providing air flow from the surroundings to thesonication chamber 22.

The airflow member 27 has an airflow bridge 27 a and an airflow duct 27b made in one piece, the airflow bridge 27 a having two airway openings27 a′ forming a portion of the inhalation channel 20 and the airflowduct 27 b extending in the sonication chamber 22 from the airflow bridge27 a for providing the air flow from the surroundings to the sonicationchamber.

The airflow bridge 27 a cooperates with the frustoconical element 20 aat the second diameter 20 a 2.

The airflow bridge 27 a has two opposite peripheral openings 27 a″providing air flow to the airflow duct 27 b.

The cooperation with the airflow bridge 27 a and the frustoconicalelement 20 a is arranged so that the two opposite peripheral openings 27a″ cooperate with complementary openings 20 a″ in the frustoconicalelement 20 a.

The mouthpiece 1 and the frustoconical element 20 a are radially spacedand an airflow chamber 28 is arranged between them.

As depicted in FIGS. 1 and 2, the mouthpiece 1 has two oppositeperipheral openings 1″.

The peripheral openings 27 a″, 20 a″, 1″ of the airflow bridge 27 a, thefrustoconical element 20 a and the mouthpiece 1 directly supply maximumair flow to the sonication chamber 22.

The frustoconical element 20 a includes an internal passage, aligned inthe similar direction as the inhalation channel 20, having a firstdiameter 20 a 1 less than that of a second diameter 20 a 2, such thatthe internal passage reduces in diameter over the frustoconical element20 a.

The frustoconical element 20 a is positioned in alignment with the meansof ultrasonic vibrations 5 and a capillary element 7, wherein the firstdiameter 20 a 1 is linked to an inner duct 11 of the mouthpiece 1 andthe second diameter 20 a 2 is linked to the inner container 20 b.

The inner container 20 b has an inner wall delimiting the sonicationchamber 22 and the liquid chamber 21.

The liquid reservoir structure 2 has an outer container 20 c delimitingthe outer wall of the liquid chamber 21.

The inner container 20 b and the outer container 20 c are respectivelythe inner wall and the outer wall of the liquid chamber 21.

The liquid reservoir structure 2 is arranged between the mouthpiece 1and the casing 3 and is detachable from the mouthpiece 1 and the casing3.

The liquid reservoir structure 2 and the mouthpiece 1 or the casing 3may include complimentary arrangements for engaging with one another;further such complimentary arrangements may include one of thefollowing: a bayonet type arrangement; a threaded engaged typearrangement; a magnetic arrangement; or a friction fit arrangement;wherein the liquid reservoir structure 2 includes a portion of thearrangement and the mouthpiece 1 or the casing 3 includes thecomplimentary portion of the arrangement.

In the reusable arrangement, the components are substantially the same.The differences in the reusable arrangement vis-a-vis the disposablearrangement are the accommodations made to replace the liquid reservoirstructure 2.

As shown in FIG. 3, the liquid chamber 21 has a top wall 23 and a bottomwall 25 closing the inner container 20 b and the outer container 20 c ofthe liquid chamber 21.

The capillary element 7 is arranged between a first section 20 b 1 and asecond section 20 b 2 of the inner container 20 b.

The capillary element 7 has a flat shape extending from the sonicationchamber to the liquid chamber.

As depicted in FIG. 2 or 3, the capillary element 7 comprises a centralportion 7 a in U-shape and a peripheral portion 7 b in L-shape.

The L-shape portion 7 b extends into the liquid chamber 21 on the innercontainer 20 b and along the bottom wall 25.

The U-shape portion 7 a is contained into the sonication chamber 21. TheU-shape portion 7 a on the inner container 20 b and along the bottomwall 25.

In the ultrasonic mist inhaler, the U-shape portion 7 a has an innerportion 7 a 1 and an outer portion 7 a 2, the inner portion 7 a 1 beingin surface contact with an atomization surface 50 of the means ofultrasonic vibrations 5 and the outer portion 7 a 2 being not in surfacecontact with the means of ultrasonic vibrations 5.

The bottom wall 25 of the liquid chamber 21 is a bottom plate 25 closingthe liquid chamber 21 and the sonication chamber 22. The bottom plate 25is sealed, thus preventing leakage of liquid from the sonication chamber22 to the casing 3.

The bottom plate 25 has an upper surface 25 a having a recess 25 b onwhich is inserted an elastic member 8. The means of ultrasonicvibrations 5 are supported by the elastic member 8. The elastic member 8is formed from an annular plate-shaped rubber having an inner hole 8′wherein a groove is designed for maintaining the means of ultrasonicvibrations 5.

The top wall 23 of the liquid chamber 21 is a cap 23 closing the liquidchamber 23.

The top wall 23 has a top surface 23 representing the maximum level ofthe liquid that the liquid chamber 21 may contain and the bottom surface25 representing the minimum level of the liquid in the liquid chamber21.

The top wall 23 is sealed, thus preventing leakage of liquid from theliquid chamber 21 to the mouthpiece 1.

The top wall 23 and the bottom wall 25 are fixed to the liquid reservoirstructure 2 by means of fixation such as screws, glue or friction.

As depicted in FIG. 3, the elastic member is in line contact with themeans of ultrasonic vibrations 5 and prevents contact between the meansof ultrasonic vibrations 5 and the inhaler walls, suppression ofvibrations of the liquid reservoir structure are more effectivelyprevented. Thus, fine particles of the liquid atomized by the atomizingmember can be sprayed farther.

As depicted in FIG. 3, the inner container 20 b has openings 20 b′between the first section 20 b 1 and the second section 20 b 2 fromwhich the capillary element 7 is extending from the sonication chamber21. The capillary element 7 absorbs liquid from the liquid chamber 21through the apertures 20 b′. The capillary element 7 is a wick. Thecapillary element 7 transports liquid to the sonication chamber 22 viacapillary action. In some arrangements, the capillary element 7 is madeof bamboo fibers. In some arrangements, the capillary element 7 may beof a thickness between 0.27 mm and 0.32 mm and have a density between 38g/m² and 48 g/m².

As can be seen in FIG. 3, the means of ultrasonic vibrations 5 aredisposed directly below the capillary element 7.

The means of ultrasonic vibrations 5 may be an ultrasonic transducer.For arrangement, the means of ultrasonic vibrations 5 may be apiezoelectric transducer, which may be designed in a circularplate-shape. The material of the piezoelectric transducer may beceramic.

A variety of transducer materials can also be used for the means ofultrasonic vibrations 5.

The end of the airflow duct 27 b 1 faces the means of ultrasonicvibrations 5. The means of ultrasonic vibrations 5 are in electricalcommunication with electrical contactors 101 a, 101 b. It is noted that,the distal end 4 b of the integrated circuit 4 has an inner electrodeand an outer electrode. The inner electrode contacts the firstelectrical contact 101 a which is a spring contact probe, and the outerelectrode contacts the second electrical contact 101 b which is a sidepin. Via the integrated circuit 4, the first electrical contact 101 a isin electrical communication with the positive terminal of the electricalstorage device 30 by way of the microprocessor, while the secondelectrical contact 101 b is in electrical communication with thenegative terminal of the electrical storage device 30.

The electrical contacts 101 a, 101 b crossed the bottom plate 25. Thebottom plate 25 is designed to be received inside the perimeter wall 26of the liquid reservoir structure 2. The bottom plate 25 rests oncomplementary ridges, thereby creating the liquid chamber 21 andsonication chamber 22.

The inner container 20 b comprises a circular inner slot 20 d on which amechanical spring is applied.

By pushing the central portion 7 a 1 onto the means of ultrasonicvibrations 5, the mechanical spring 9 ensures a contact surface betweenthem.

The liquid reservoir structure 2 and the bottom plate 25 can be madeusing a variety of thermoplastic materials.

When the user draws on the ultrasonic mist inhaler 100, an air flow isdrawn from the peripheral openings 1″ and penetrates the airflow chamber28, passes the peripheral openings 27 a″ of the airflow bridge 27 a andthe frustoconical element 20 a and flows down into the sonicationchamber 22 via the airflow duct 27 b directly onto the capillary element7. At the same time, the liquid is drawn from the reservoir chamber 21by capillarity, through the plurality of apertures 20 b′, and into thecapillary element 7. The capillary element 7 brings the liquid intocontact with the means of ultrasonic vibrations 5 of the inhaler 100.The user's draw also causes the pressure sensor to activate theintegrated circuit 4, which directs current to the means of ultrasonicvibrations 5. Thus, when the user draws on the mouthpiece 1 of theinhaler 100, two actions happen at the same time. Firstly, the sensoractivates the integrated circuit 4, which triggers the means ofultrasonic vibrations 5 to begin vibrating. Secondly, the draw reducesthe pressure outside the reservoir chamber 21 such that flow of theliquid through the apertures 20 b′ begins, which saturates the capillaryelement 7. The capillary element 7 transports the liquid to the means ofultrasonic vibrations 5, which causes bubbles to form in a capillarychannel by the means of ultrasonic vibrations 5 and mist the liquid.Then, the mist liquid is drawn by the user.

In some arrangements, the integrated circuit 4 comprises a frequencycontroller which is configured to control the frequency at which themeans of ultrasonic vibrations 5 operates. The frequency controllercomprises a processor and a memory, the memory storing executableinstructions which, when executed by the processor, cause the processorto perform at least one function of the frequency controller.

As described above, in some arrangements the ultrasonic mist inhaler 100drives the means of ultrasonic vibrations 5 with a signal having afrequency of 2.8 MHz to 3.2 MHz in order to vaporize a liquid having aliquid viscosity of 1.05 Pa·s to 1.412 Pa·s in order to produce a bubblevolume of about 0.25 to 0.5 microns. However, for liquids with adifferent viscosity or for other applications it the means of ultrasonicvibrations 5 may be driven at a different frequency.

For each different application for a mist generation system, there is anoptimum frequency or frequency range for driving the means of ultrasonicvibrations 5 in order to optimize the generation of mist. Inarrangements where the means of ultrasonic vibrations 5 is apiezoelectric transducer, the optimum frequency or frequency range willdepend on at least the following four parameters:

1. Transducer Manufacturing Processes

In some arrangements, the means of ultrasonic vibrations 5 comprises apiezoelectric ceramic. The piezoelectric ceramic is manufactured bymixing compounds to make a ceramic dough and this mixing process may notbe consistent throughout production. This inconsistency can give rise toa range of different resonant frequencies of the cured piezoelectricceramic.

If the resonant frequency of the piezoelectric ceramic does notcorrespond to the required frequency of operation of the device then nomist is produced during the operation of the device. In the case of anicotine mist inhaler, even a slight offset in the resonant frequency ofthe piezoelectric ceramic is enough to impact the production of mist,meaning that the device will not deliver adequate nicotine levels to theuser.

2. Load on Transducer

During operation, any changes in the load on the piezoelectrictransducer will inhibit the overall displacement of the oscillation ofthe piezoelectric transducer. To achieve optimal displacement of theoscillation of the piezoelectric transducer, the drive frequency must beadjusted to enable the circuit to provide adequate power for maximumdisplacement.

The types of loads that can affect the oscillator's efficiency caninclude the amount of liquid on the transducer (dampness of the wickingmaterial), and the spring force applied to the wicking material to keeppermanent contact with the transducer. It may also include the means ofelectrical connection.

3. Temperature

Ultrasonic oscillations of the piezoelectric transducer are partiallydamped by its assembly in a device. This may include the transducerbeing placed in a silicone/rubber ring, and the spring exerting pressureonto the wicking material that is above the transducer. This dampeningof the oscillations causes rise in local temperatures on and around thetransducer.

An increase in temperature affects the oscillation due to changes in themolecular behavior of the transducer. An increase in the temperaturemeans more energy to the molecules of the ceramic, which temporarilyaffects its crystalline structure. Although the effect is reversed asthe temperature reduces, a modulation in supplied frequency is requiredto maintain optimal oscillation. This modulation of frequency cannot beachieved with a conventional fixed frequency device.

An increase in temperature also reduces the viscosity of the solution(e-liquid) which is being vaporized, which may require an alteration tothe drive frequency to induce cavitation and maintain continuous mistproduction. In the case of a conventional fixed frequency device, areduction in the viscosity of the liquid without any change in the drivefrequency will reduce or completely stop mist production, rendering thedevice inoperable.

4. Distance to Power Source

The oscillation frequency of the electronic circuit can change dependingon the wire-lengths between the transducer and the oscillator-driver.The frequency of the electronic circuit is inversely proportional to thedistance between the transducer and the remaining circuit.

Although the distance parameter is primarily fixed in a device, it canvary during the manufacturing process of the device, reducing theoverall efficiency of the device. Therefore, it is desirable to modifythe drive frequency of the device to compensate for the variations andoptimize the efficiency of the device.

A piezoelectric transducer can be modelled as an RLC circuit in anelectronic circuit, as shown in FIG. 5. The four parameters describedabove may be modelled as alterations to the overall inductance,capacitance, and/or resistance of the RLC circuit, changing theresonance frequency range supplied to the transducer. As the frequencyof the circuit increases to around the resonance point of thetransducer, the log Impedance of the overall circuit dips to a minimumand then rises to a maximum before settling to a median range.

FIG. 6 shows a generic graph explaining the change in overall impedancewith increase in frequency in an RLC circuit. FIG. 7 shows how apiezoelectric transducer acts as a capacitor in a first capacitiveregion at frequencies below a first predetermined frequency f_(s) and ina second capacitive region at frequencies above a second predeterminedfrequency f_(p). The piezoelectric transducer acts as an inductor in aninductive region at frequencies between the first and secondpredetermined frequencies f_(s), f_(p). In order to maintain optimaloscillation of the transducer and hence maximum efficiency, the currentflowing through the transducer must be maintained at a frequency withinthe inductive region.

The frequency controller of the device of some arrangements isconfigured to maintain the frequency of oscillation of the piezoelectrictransducer (the means of ultrasonic vibrations 5) within the inductiveregion, in order to maximize the efficiency of the device.

The frequency controller is configured to perform a sweep operation inwhich the frequency controller drives the transducer at frequencieswhich track progressively across a predetermined sweep frequency range.As the frequency controller performs the sweep, the frequency controllermonitors an Analog-to-Digital Conversion (ADC) value of anAnalog-to-Digital converter which is coupled to the transducer. In somearrangements the ADC value is a parameter of the ADC which isproportional to the voltage across the transducer. In otherarrangements, the ADC value is a parameter of the ADC which isproportional to the current flowing through the transducer.

As will be described in more detail below, the frequency controller ofsome arrangements determines the active power being used by theultrasonic transducer by monitoring the current flowing through thetransducer.

During the sweep operation, the frequency controller locates theinductive region of the frequency for the transducer. Once the frequencycontroller has identified the inductive region, the frequency controllerrecords the ADC value and locks the drive frequency of the transducer ata frequency within the inductive region (i.e. between the first andsecond predetermined frequencies f_(s), f_(p)) in order to optimize theultrasonic cavitation by the transducer. When the drive frequency islocked within the inductive region, the electromechanical couplingfactor of the transducer is maximized, thereby maximizing the efficiencyof the device.

In some arrangements, the frequency controller is configured to performthe sweep operation to locate the inductive region each time theoscillation is started or re-started. In the arrangements, the frequencycontroller is configured to lock the drive frequency at a new frequencywithin the inductive region each time the oscillation is started andthereby compensate for any changes in the parameters that affect theefficiency of operation of the device.

In some arrangements, the frequency controller ensures optimal mistproduction and maximizes efficiency of medication delivery to the user.In some arrangements, the frequency controller optimizes the device andimproves the efficiency and maximizes nicotine delivery to the user.

In other arrangements, the frequency controller optimizes the device andimproves the efficiency of any other device which uses ultrasound. Insome arrangements, the frequency controller is configured for use withultrasound technology for therapeutic applications in order to extendthe enhancement of drug release from an ultrasound-responsive drugdelivery system. Having precise, optimal frequency during operation,ensures that the microbubbles, nanobubbles, nanodroplets, liposome,emulsions, micelles or any other delivery systems are highly effective.

In some arrangements, in order to ensure optimal mist generation andoptimal delivery of compounds as described above, the frequencycontroller is configured to operate in a recursive mode. When thefrequency controller operates in the recursive mode, the frequencycontroller runs the sweep of frequencies periodically during theoperation of the device and monitors the ADC value to determine if theADC value is above a predetermined threshold which is indicative ofoptimal oscillation of the transducer.

In some arrangements, the frequency controller runs the sweep operationwhile the device is in the process of aerosolizing liquid in case thefrequency controller is able to identify a possible better frequency forthe transducer. If the frequency controller identifies a betterfrequency, the frequency controller locks the drive frequency at thenewly identified better frequency in order to maintain optimal operationof the device.

In some arrangements, the frequency controller runs the sweep offrequencies for a predetermined duration periodically during theoperation of the device. In the case of the device of the arrangementsdescribed above, the predetermined duration of the sweep and the timeperiod between sweeps are selected to optimize the functionality of thedevice. When implemented in an ultrasonic mist inhaler device, this willensure an optimum delivery to a user throughout the user's inhalation.

FIG. 8 shows a flow diagram of the operation of the frequency controllerof some arrangements.

The following disclosure discloses further arrangements of mistgenerator devices which comprise many of the same elements as thearrangements described above. Elements of the arrangements describedabove may be interchanged with any of the elements of the arrangementsdescribed in the remaining part of this disclosure.

The mist generator devices described below are used with or are for usewith a hookah device 202 which is also described below. In otherarrangements, the hookah device 202 comprises a plurality of other mistgenerator devices instead of the mist generator device 201 describedherein.

To ensure adequate aerosol production, the mist generator device 201 ofsome arrangements comprises an ultrasonic/piezoelectric transducer ofexactly or substantially 16 mm diameter. This transducer is manufacturedto specific capacitance and impedance values to control the frequencyand power required for desired aerosol volume production.

A horizontally placed disc-shaped 16 mm diameter ultrasonic transducerwould result in a large mist generator device. To minimize the size, theultrasonic transducer of this arrangement is held vertically in thesonication chamber (the planar surface of the ultrasonic transducer isgenerally parallel with the flow of aerosol mist and/or generallyparallel to the longitudinal length of the mist generator device). Putanother way, the ultrasonic transducer is generally perpendicular to abase of the mist generator device.

Referring now to FIGS. 9 to 11 of the accompanying drawings, the mistgenerator device 201 comprises a mist generator housing 204 which iselongate and optionally formed from two housing portions 205, 206 whichare attached to one another. The mist generator housing 204 comprises anair inlet port 207 and a mist outlet port 208.

In this arrangement, the mist generator housing 204 is of injectionmolded plastic, specifically polypropylene that is typically used formedical applications. In this arrangement, the mist generator housing204 is of a heterophasic copolymer. More particularly a BF970MOheterophasic copolymer, which has an optimum combination of very highstiffness and high impact strength. The mist generator housing partsmolded with this material exhibit good anti-static performance.

A heterophasic copolymer such as polypropylene is particularly suitablefor the mist generator housing 204 since this material does not causecondensation of the aerosol as it flows from the sonication chamber 219through the mist outlet port 208. This plastic material can also bedirectly recycled easily using industrial shredding and cleaningprocesses.

In FIG. 10, the mist outlet port 208 is closed by a closure element 209.However, it is to be appreciated that when the mist inhaler device 200is in use, the closure element 209 is removed from the mist outlet port208, as shown in FIG. 9.

Referring now to FIGS. 12 and 13, the mist generator device 200comprises a transducer holder 210 which is held within the mistgenerator housing 204. The transducer holder 210 comprises a bodyportion 211 which, in this arrangement, is cylindrical or generallycylindrical in shape with circular upper and lower openings 212, 213.The transducer holder 210 is provided with an internal channel 214 forreceiving an edge of an ultrasonic transducer 215, as shown in FIG. 13.

The transducer holder 210 incorporates a cutaway section 216 throughwhich an electrode 217 extends from the ultrasonic transducer 215 sothat the electrode 217 may be connected electrically to an AC driver ofthe hookah device 202, as described in more detail below.

Referring again to FIG. 11, the mist generator device 201 comprises aliquid chamber 218 which is provided within the mist generator housing204. The liquid chamber 218 is for containing a liquid to be atomized.In some arrangements, a liquid is contained in the liquid chamber 218.In other arrangements, the liquid chamber 218 is empty initially and theliquid chamber is filled with a liquid subsequently.

A liquid (also referred to herein as an e-liquid) composition suitablefor use in an ultrasonic mist generator device 201 of some arrangementsconsists of a nicotine salt consisting of nicotine levulinate wherein:

The relative amount of vegetable glycerin in the composition is: from 55to 80% (w/w), or from 60 to 80% (w/w), or from 65 to 75% (w/w), or 70%(w/w); and/or,

The relative amount of propylene glycol in the composition is: from 5 to30% (w/w), or from 10 to 30% (w/w), or from 15 to 25% (w/w), or 20%(w/w); and/or,

The relative amount of water in the composition is: from 5 to 15% (w/w),or from 7 to 12% (w/w), or 10% (w/w); and/or,

The amount of nicotine and/or nicotine salt in the composition is: from0.1 to 80 mg/ml, or from 0.1 to 50 mg/ml, or from 1 to 25 mg/ml, or from10 to 20 mg/ml, or 17 mg/ml.

In some arrangements, the mist generator device 201 contains an e-liquidhaving a kinematic viscosity between 1.05 Pa·s and 1.412 Pa·s.

In some arrangements, the liquid chamber 218 contains a liquidcomprising a nicotine levulinate salt at a 1:1 molar ratio.

In some arrangements, the liquid chamber 218 contains an e-liquidcomprising nicotine, propylene glycol, vegetable glycerin, water andflavorings. In some examples, the % concentration of each component inthe e-liquid is shown below in Table 1, Table 2, Table 3 or Table 4.

TABLE 1 The % concentration of each component in the e-liquid (e-liquid1). Component % (w/w) Propylene glycol 15.1 Vegetable glycerin 70 Water10 Nicotine 1.7 Levulinic acid 0.2 Flavorings 3

TABLE 2 The % concentration of each component in the e-liquid (e-liquid2) (Approximately, 2:1 molar ratio of levulinic acid to nicotine.)Component % (w/w) Propylene glycol 12.87 Vegetable glycerin 70 Water 10Nicotine 1.7 Levulinic acid 2.43 Flavorings 3

TABLE 3 The % concentration of each component in the e-liquid (e-liquid3) (Approximately, 1:1 molar ratio of levulinic acid to nicotine.)Component % (w/w) Propylene glycol 14.08 Vegetable glycerin 70 Water 10Nicotine 1.7 Levulinic acid 1.22 Flavorings 3

TABLE 4 The % concentration of each component in the e-liquid (e-liquid4) (Approximately, 3:1 molar ratio of levulinic acid to nicotine.)Component % (w/w) Propylene glycol 11.64 Vegetable glycerin 70 Water 10Nicotine 1.7 Levulinic acid 3.66 Flavorings 3

In the non-limiting examples, the nicotine in solution is all or part inthe form of nicotine levulinate.

The nicotine levulinate salt is formed by combining nicotine andlevulinic acid in solution. This results in the formation of the saltnicotine levulinate, which comprises a levulinate anion and a nicotinecation.

The % concentration of nicotine in the e-liquid shown in Table 1, Table2, Table 3 and Table 4 is approximately equivalent to 17 mg/ml.

In some arrangements, the liquid chamber 218 contains a liquid having akinematic viscosity between 1.05 Pa·s and 1.412 Pa·s and a liquiddensity between 1.1 g/ml and 1.3 g/ml.

In some arrangements, the liquid within the liquid chamber 218 comprisesa flavoring (e.g. a fruit flavor) which is tasted by a user when theuser inhales mist generated by the hookah device.

By using an e-liquid with the correct parameters of viscosity, densityand having a desired target bubble volume of liquid spray into the air,it has been found that the frequency range of 2.8 MHz to 3.2 MHz forliquid viscosity range of 1.05 Pa·s and 1.412 Pa·s and density ofapproximately 1.1-1.3 g/mL (get density ranges from Hertz) produce adroplet volume where 90% of droplets are below 1 micron and 50% of thoseare less than 0.5 microns.

The mist generator device 201 comprises a sonication chamber 219 whichis provided within the mist generator housing 204.

Returning to FIGS. 12 and 13, the transducer holder 210 comprises adivider portion 220 which provides a barrier between the liquid chamber218 and the sonication chamber 219. The barrier provided by the dividerportion 220 minimizes the risk of the sonication chamber 219 being isflooded with liquid from the liquid chamber 218 or for a capillaryelement over the ultrasonic transducer 215 becoming oversaturated,either of which would overload and reduce the efficiency of theultrasonic transducer 215. Moreover, flooding the sonication chamber 219or over saturating the capillary element could also cause an unpleasantexperience with the liquid being sucked in by the user duringinhalation. To mitigate this risk, the divider portion 220 of thetransducer holder 210 sits as a wall between the sonication chamber 219and the liquid chamber 218.

The divider portion 220 comprises a capillary aperture 221 which is theonly means by which liquid can flow from the liquid chamber 218 to thesonication chamber 219, via a capillary element. In this arrangement,the capillary aperture 221 is an elongate slot having a width of 0.2 mmto 0.4 mm. The dimensions of the capillary aperture 221 are such thatthe edges of the capillary aperture 221 provide a biasing force whichacts on a capillary element extending through the capillary aperture 221for added control of liquid flow to the sonication chamber 219.

In this arrangement, the transducer holder 210 is of liquid siliconerubber (LSR). In this arrangement, the liquid silicone rubber has aShore A 60 hardness. This LSR material ensures that the ultrasonictransducer 215 vibrates without the transducer holder 210 dampening thevibrations. In this arrangement, the vibratory displacement of theultrasonic transducer 215 is 2-5 nanometers and any dampening effect mayreduce the efficiency of the ultrasonic transducer 215. Hence, this LSRmaterial and hardness is selected for optimal performance with minimalcompromise.

Referring now to FIGS. 14 and 15, the mist generator device 201comprises a capillary or capillary element 222 for transferring a liquid(containing a drug or other substance) from the liquid chamber 218 tothe sonication chamber 219. The capillary element 222 is planar orgenerally planar with a first portion 223 and a second portion 224. Inthis arrangement, the first portion 223 has a rectangular or generallyrectangular shape and the second portion 224 has a partly circularshape.

In this arrangement, the capillary element 222 comprises a third portion225 and a fourth portion 226 which are respectively identical in shapeto the first and second portions 223, 224. The capillary element 222 ofthis arrangement is folded about a fold line 227 such that the first andsecond portions 223, 224 and the third and fourth portions 225, 226 aresuperimposed on one another, as shown in FIG. 15.

In this arrangement, the capillary element has a thickness ofapproximately 0.28 mm. When the capillary element 222 is folded to havetwo layers, as shown in FIG. 15, the overall thickness of the capillaryelement is approximately 0.56 mm. This double layer also ensures thatthere is always sufficient liquid on the ultrasonic transducer 215 foroptimal aerosol production.

In this arrangement, when the capillary element 222 is folded, the lowerend of the first and third parts 223, 225 defines an enlarged lower end228 which increases the surface area of the capillary element 222 in theportion of the capillary element 222 which sits in liquid within theliquid chamber 218 to maximize the rate at which the capillary element222 absorbs liquid.

In this arrangement, the capillary element 222 is 100% bamboo fiber. Inother arrangements, the capillary element is of at least 75% bamboofiber. The benefits of using bamboo fiber as the capillary element areas described above.

Referring now to FIGS. 16 and 17, the capillary element 222 is retainedby the transducer holder 210 such that the transducer holder 210 retainsthe second portion 224 of the capillary element 222 superimposed on partof an atomization surface of the ultrasonic transducer 215. In thisarrangement, the circular second portion 224 sits within the innerrecess 214 of the transducer holder 210.

The first portion 223 of the capillary element 222 extends through thecapillary aperture 221 in the transducer holder 210.

Referring now to FIGS. 18 to 20, the second portion 206 of the mistgenerator housing 204 comprises a generally circular wall 229 whichreceives the transducer holder 222 and forms part of the wall of thesonication chamber 219.

Contact apertures 230 and 231 are provided in a side wall of the secondportion 206 for receiving electrical contacts 232 and 233 which formelectrical connections with the electrodes of the ultrasonic transducer215.

In this arrangement, an absorbent tip or absorbent element 234 isprovided adjacent the mist outlet port 208 to absorb liquid at the mistoutlet port 208. In this arrangement, the absorbent element 234 is ofbamboo fiber.

Referring now to FIGS. 21 to 23, the first portion 205 of the mistgenerator housing 204 is of a similar shape to the second portion 206and comprises a further generally circular wall portion 235 which formsa further portion of the wall of the sonication chamber 219 and retainsthe transducer holder 210.

In this arrangement, a further absorbent element 236 is providedadjacent the mist outlet port 208 to absorb liquid at the mist outletport 208.

In this arrangement, the first portion 205 of the mist generator housing204 comprises a spring support arrangement 237 which supports the lowerend of a retainer spring 238, as shown in FIG. 24.

An upper end of the retainer spring 238 contacts the second portion 224of the capillary element 222 such that the retainer spring 238 providesa biasing force which biases the capillary element 222 against theatomization surface of the ultrasonic transducer 215.

Referring to FIG. 25, the transducer holder 210 is shown in position andbeing retained by the second portion 206 of the mist generator housing204, prior to the two portions 205, 206 of the mist generator housing204 being attached to one another.

Referring to FIGS. 26 to 29, in this arrangement, the mist generatordevice 201 comprises an identification arrangement 239. Theidentification arrangement 239 comprises a printed circuit board 240having electrical contacts 241 provided on one side and an integratedcircuit 242 and another optional component 243 provided on the otherside.

The integrated circuit 242 has a memory which stores a unique identifierfor the mist generator device 201. The electrical contacts 241 providean electronic interface for communication with the integrated circuit242.

The printed circuit board 240 is, in this arrangement, mounted within arecess 244 on one side of the mist generator housing 204. The integratedcircuit 242 and optional other electronic components 243 sit within afurther recess 245 so that the printed circuit board 240 is generallyflush with the side of the mist generator housing 204.

In this arrangement, the integrated circuit 242 is aone-time-programmable (OTP) device which provides an anti-counterfeitingfeature that allows only genuine mist generator devices from themanufacturer to be used with the device. This anti-counterfeitingfeature is implemented in the mist generator device 201 as a specificcustom integrated circuit (IC) that is bonded (with the printed circuitboard 240) to the mist generator device 201. The OTP as IC contains atruly unique information that allows a complete traceability of the mistgenerator device 201 (and its content) over its lifetime as well as aprecise monitoring of the consumption by the user. The OTP IC allows themist generator device 201 to function to generate mist only whenauthorized.

The OTP, as a feature, dictates the authorized status of a specific mistgenerator device 201. Indeed, in order to prevent emissions of carbonylsand keep the aerosol at safe standards, experiments have shown that themist generator device 201 is considered empty of liquid in the liquidchamber 218 after approximately 1,000 seconds of aerosolization. In thatway a mist generator device 201 that is not genuine or empty will not beable to be activated after this predetermined duration of use.

The OTP, as a feature, may be part of a complete chain with theconjunction of the digital sale point, the mobile companion applicationand the mist generator device 201. Only a genuine mist generator device201 manufactured by a trusted party and sold on the digital sale pointcan be used in the hookah device 202. The OTP IC is read by the hookahdevice 202 which recognizes the mist generator device 201.

In some arrangements, the OTP IC is disposable in the same way as themist generator device 201. Whenever the mist generator device 201 isconsidered empty, it will not be activated if inserted into a hookahdevice 202. Similarly, a counterfeit mist generator device 201 would notbe functional in the hookah device 202.

Referring now to FIG. 30 of the accompanying drawings, the hookah device202 comprises a plurality of ultrasonic transducer driver microchips,each of which is referred to herein as a power management integratedcircuit or PMIC 300. Each PMIC 300 is a microchip for driving arespective ultrasonic transducer 215 in one of the mist generatordevices 201. In examples of this disclosure, the number of PMICs in thehookah device 202 corresponds to the number of mist generator devices201 that are for use with the hookah device 202. In the exampledescribed below, there are four mist generator devices 201 and thehookah device 202 comprises four corresponding PMICs 300. In otherexamples, the hookah device 202 comprises two to eight PMICs 300 whichare configured to drive two to eight mist generator devices 201 that arecoupled to the hookah device 202.

In this disclosure, the terms chip, microchip and integrated circuit areinterchangeable. The microchip or integrated circuit is a single unitwhich comprises a plurality of interconnected embedded components andsubsystems. The microchip is, for example, at least partly of asemiconductor, such as silicon, and is fabricated using semiconductormanufacturing techniques.

The hookah device 202 also comprises a plurality of second microchips,each of which is referred to herein as a bridge integrated circuit orbridge IC 301. Each bridge IC 301 is electrically connected a respectiveone of the PMICs 300. Each bridge IC 301 is a microchip for driving arespective ultrasonic transducer 215 in one of the mist generatordevices 201. In examples of this disclosure, the number of bridge ICs301 in the hookah device 202 corresponds to the number of mist generatordevices 201 that are for use with the hookah device 202. Each bridge IC301 is a single unit which comprises a plurality of interconnectedembedded components and subsystems. In the example described below,there are four bridge ICs 301 and the hookah device 202 comprises fourcorresponding PMICs 300.

In this example, each PMIC 300 its respective connected bridge IC 301are mounted to the same PCB of the hookah device 202. As describedbelow, each bridge IC 301 is connected to its respective PMIC 300 viaconnections on a PCB and not via a communications bus (e.g. the I2C busdescribed below). In this example, the physical dimensions of the PMIC300 are 1-3 mm wide and 1-3 mm long and the physical dimensions of thebridge IC 301 are 1-3 mm wide and 1-3 mm long.

For simplicity, FIG. 43 shows only one PMIC 300 and one bridge IC 301and the following description refers to only one PMIC 300 and one bridgeIC 301. However, it is to be appreciated that the hookah device 202incorporates a plurality of PMICs 300 and a plurality of respectivebridge ICs 301 which are connected in the same configuration as shown inFIG. 43. As described below, each PMIC 300 is connected to acommunications (I2C) bus 302 so that each PMIC 300 can be controlledindependently by signals from a microcontroller 303 which are sent viathe communications bus 302.

As described above, the mist generator device 201 comprises aprogrammable or one time programmable integrated circuit or OTP IC 242.When the mist generator device 201 is coupled to the hookah device 202,the OTP IC is electrically connected to the PMIC 300 to receive powerfrom the PMIC 300 such that the PMIC 300 can manage the voltage suppliedto the OTP IC 242. The OTP IC 242 is also connected to a data bus orcommunications bus 302 in the hookah device 202. In this example, thecommunications bus 302 is an I2C bus but in other examples thecommunications bus 302 is another type of data bus.

The ultrasonic transducer 215 in the mist generator device 201 iselectrically connected to the bridge IC 301 so that the ultrasonictransducer 215 may be driven by an AC drive signal generated by thebridge IC 301 when the hookah device 202 is in use.

The hookah device 202 comprises a processor in the form of themicrocontroller 303 which is electrically coupled for communication withthe communication bus 302. In this example, the microcontroller 303 is aBluetooth™ low energy (BLE) microcontroller. The microcontroller 303receives power from a low dropout regulator (LDO) 304 which is driven bya battery or, in this example, from an external power supply. The LDO304 provides a stable regulated voltage to the microcontroller 303 toenable the microcontroller 303 to operate consistently even when thereis a variation in the voltage of the battery or other power supply.

The hookah device 202 comprises a voltage regulator in the form of aDC-DC boost converter 305 which is powered by the battery or an externalpower supply. Only one DC-DC boost converter 305 is shown in FIG. 43 butin some examples the hookah device 202 comprises a plurality of DC-DCboost converters 305 which each supply power to a respective one of theplurality of bridge ICs 301. In other examples, the hookah device 305comprises only one DC-DC boost converter 305 which is configured tosupply power to each of the plurality of bridge ICs 301.

The boost converter 305 increases the voltage of the battery or powersupply to a programmable voltage VBOOST. The programmable voltage VBOOSTis set by the boost converter 305 in response to a voltage controlsignal VCTL from the PMIC 300. As will be described in more detailbelow, the boost converter 305 outputs the voltage VBOOST to the bridgeIC 301. In other examples, the voltage regulator is a buck converter oranother type of voltage regulator which outputs a selectable voltage.

The voltage control signal VCTL is generated by a digital to analogueconverter (DAC) which, in this example, is implemented within the PMIC300. The DAC is not visible in FIG. 30 since the DAC is integratedwithin the PMIC 300. The DAC and the technical benefits of integratingthe DAC within the PMIC 300 are described in detail below.

In this example, the PMIC 300 is connected to a power source connector306 so that the PMIC 300 can receive a charging voltage VCHRG when thepower source connector 306 is coupled to a USB charger. In otherexamples, the PMIC 300 is connected to a different power socket whichenables the hookah device 202 to be connected to and be powered by anexternal power source.

The hookah device 202 comprises a first pressure sensor 307 which, inthis example, is a static pressure sensor. The hookah device 202 alsocomprises a second pressure sensor 308 which, in this example, is adynamic pressure sensor. However, in other examples, the hookah device202 comprises only one of the two pressure sensors 307, 308. Thepressure sensors 307, 308 sense a change in air pressure to sense when auser is drawing on the hookah and drawing air through the mist generatordevice 201.

In this example, the hookah device 202 comprises a plurality of LEDs 308which are controlled by the PMIC 300. In other examples, one or more ofthe LEDs 308 are omitted.

The microcontroller 303 functions as a master device on thecommunications bus 302, with the PMIC 300 being a first slave device,the OTP IC 242 being a second slave device, the second pressure sensor308 being a third slave device and the first pressure sensor 307 beingthe a fourth slave device. Each additional PMIC 300 of the plurality ofPMICs 300 is another slave device on the communications bus 302. Thecommunication bus 302 enables the microcontroller 303 to control thefollowing functions within the hookah device 202:

-   -   1. All functions of each PMIC 300 are highly configurable by the        microcontroller 303.    -   2. The current flowing through the ultrasonic transducer 215 is        sensed by a high bandwidth sense and rectifier circuit at a high        common mode voltage (high side of the bridge). The sensed        current is converted into a voltage proportional to the rms        current and provided as a buffered voltage at a current sense        output pin 309 of the bridge IC 301. This voltage is fed to and        sampled in the PMIC 300 and made available as a digital        representation via I2C requests. Sensing the current flowing        through the ultrasonic transducer 215 forms part of the resonant        frequency tracking functionality. As described herein, the        ability of the device to enable this functionality within the        bridge IC 301 provides significant technical benefits.    -   3. The DAC (not shown in FIG. 30) integrated within the PMIC 300        enables the DC-DC boost converter voltage VBOOST to be        programmed to be between 10V and 20V.    -   4. The microcontroller 303 enables the charger sub-system of the        device 202 to manage the charging of a battery, which may be is        a single cell battery.    -   5. A Light Emitting Diode (LED) driver module (not shown) is        powered by the PMIC 300 to drive and dim digitally the LEDs 308        either in linear mode or in gamma corrected mode.    -   6. The microcontroller 303 is able to read Pressure #1 and        Pressure #2 sensor values from the pressure sensors 307, 308.

Referring now to FIG. 31 of the accompanying drawings, each PMIC 300 is,in this example, a self-contained chip or integrated circuit whichcomprises integrated subsystems and a plurality of pins which provideelectrical inputs and outputs to the PMIC 300. The references to anintegrated circuit or chip in this disclosure are interchangeable andeither term encompasses a semiconductor device which may, for instance,be of silicon.

The PMIC 300 comprises an analogue core 310 which comprises analoguecomponents including a reference block (BG) 311, a LDO 312, a currentsensor 313, a temperature sensor 314 and an oscillator 315.

As described in more detail below, the oscillator 315 is coupled to adelay locked loop (DLL) which outputs pulse width modulation (PWM)phases A and B. The oscillator 315 and the DLL generate a two phasecentre aligned PWM output which drives an H bridge in the bridge IC 301.

The DLL comprises a plurality of delay lines connected end to end,wherein the total delay of the delay lines is equal to the period of themain clock signal clk_m. In this example, the DLL is implemented in adigital processor subsystem, referred to herein as a digital core 316,of the PMIC 300 which receives a clock signal from the oscillator 315and a regulated power supply voltage from the LDO 312. The DLL isimplemented in a large number (e.g. in the order of millions) of delaygates which are connected end to end in the digital core 316.

The implementation of the oscillator 315 and the DLL in the sameintegrated circuit of the PMIC 300 in order to generate a two phasecentre aligned PWM signal is unique since at present no signal generatorcomponent in the integrated circuit market comprises thisimplementation.

As described herein, PWM is part of the functionality which enables thehookah device 202 to track the resonant frequency of the ultrasonictransducer 215 accurately in order to maintain an efficient transferfrom electrical energy to kinetic energy in order to optimise thegeneration of mist.

In this example, the PMIC 300 comprises a charger circuit 317 whichcontrols the charging of a battery, for instance by power from a USBpower source.

The PMIC 300 comprises an integrated power switch VSYS which configuresthe PMIC 300 to power the analogue core 310 by power from a battery orby power from an external power source.

The PMIC 300 comprises an embedded analogue to digital converter (ADC)subsystem 318. The implementation of the ADC 318 together with theoscillator 315 in the same integrated circuit is, in itself, uniquesince there is no other integrated circuit in the integrated circuitmarket which comprises an oscillator and an ADC implemented assub-blocks within the integrated circuit. In a conventional device, anADC is typically provided as a separate discrete component from anoscillator with the separate ADC and oscillator being mounted to thesame PCB. The problem with this conventional arrangement is that the twoseparate components of the ADC and the oscillator take up spaceunnecessarily on the PCB. A further problem is that the conventional ADCand oscillator are usually connected to one another by a serial datacommunication bus, such as an I2C bus, which has a limited communicationspeed of up to only 400 kHz. In contrast to conventional devices, thePMIC 300 comprises the ADC 318 and the oscillator 315 integrated withinthe same integrated circuit which eliminates any lag in communicationbetween the ADC 318 and the oscillator 315, meaning that the ADC 318 andthe oscillator 315 can communicate with one another at high speed, suchas at the speed of the oscillator 315 (e.g. 3 MHz to 5 MHz).

In the PMIC 300 of this example, the oscillator 315 is running at 5 MHzand generates a clock signal SYS CLOCK at 5 MHz. However, in otherexamples, the oscillator 315 generates a clock signal at a much higherfrequency of up to 105 MHz. The integrated circuits described herein areall configured to operate at the high frequency of the oscillator 315.

The ADC 318 comprises a plurality of feedback input terminals oranalogue inputs 319 which comprise a plurality of GPIO inputs(IF_GPIO1-3). At least one of the feedback input terminals or theanalogue inputs 319 receives a feedback signal from an H-bridge circuitin the bridge IC 301, the feedback signal being indicative of aparameter of the operation of the H-bridge circuit or an AC drive signalwhen the H-bridge circuit is driving a resonant circuit, such as theultrasonic transducer 215, with the AC drive signal. As described below,the GPIO inputs are used to receive a current sense signal from thebridge IC 301 which is indicative of the route mean square (rms) currentreported by the bridge IC 301. In this example, one of the GPIO inputsis a feedback input terminal which receives a feedback signal from theH-bridge in the bridge IC 301.

The ADC subsystem 318 samples analogue signals received at the pluralityof ADC input terminals 319 at a sampling frequency which is proportionalto the frequency of the main clock signal. The ADC subsystem 318 thengenerates ADC digital signals using the sampled analogue signals.

In this example, the ADC 318 which is incorporated in the PMIC 300samples not only the RMS current flowing through the H-bridge 334 andthe ultrasonic transducer 215 but also voltages available in the system(e.g. VBAT, VCHRG, VBOOST), the temperature of the PMIC 300, thetemperature of a battery and the GPIO inputs (IF_GPIO1-3) which allowfor future extensions.

The digital core 316 receives the ADC generated digital signals from theADC subsystem and processes the ADC digital signals to generate thedriver control signal. The digital core 316 communicates the drivercontrol signal to the PWM signal generator subsystem (DLL 332) tocontrol the PWM signal generator subsystem.

Rectification circuits existing in the market today have a very limitedbandwidth (typically less than 1 MHz). Since the oscillator 315 of thePMIC 300 is running at up to 5 MHz or even up to 105 Mhz, a highbandwidth rectifier circuit is implemented in the PMIC 300. As will bedescribed below, sensing the RMS current within an H bridge of thebridge IC 301 forms part of a feedback loop which enables the hookahdevice 202 to drive the ultrasonic transducer 215 with high precision.The feedback loop is a game changer in the industry of drivingultrasound transducers since it accommodates for any process variationin the piezo electric transducer production (variations of resonancefrequencies) and it compensates for temperature effects of the resonancefrequency. This is achieved, in part, by the inventive realisation ofintegrating the ADC 318, the oscillator 315 and the DLL within the sameintegrated circuit of the PMIC 300. The integration enables thesesub-systems to communicate with one another at high speed (e.g. at theclock frequency of 5 MHz or up to 105 MHz). Reducing the lag betweenthese subsystems is a game changer in the ultrasonics industry,particularly in the field of mist generator devices.

The ADC 318 comprises a battery voltage monitoring input VBAT and acharger input voltage monitoring input VCHG as well as voltagemonitoring inputs VMON and VRTH as well as a temperature monitoringinput TEMP.

The temperature monitoring input TEMP receives a temperature signal fromthe temperature sensor 314 which is embedded within the PMIC 300. Thisenables the PMIC 300 to sense the actual temperature within the PMIC 300accurately so that the PMIC 300 can detect any malfunction within thePMIC 300 as well as malfunction to other components on the printedcircuit board which affect the temperature of the PMIC 300. The PMIC 300can then control the bridge IC 301 to prevent excitation of theultrasonic transducer 215 if there is a malfunction in order to maintainthe safety of the mist inhaler device 200 and hence the safety of thehookah device 202.

The additional temperature sensor input VRTH receives a temperaturesensing signal from an external temperature sensor within the hookahdevice 202 which monitors the temperature of within the hookah device202. The PMIC 300 can thus react to shut down the hookah device 202 inorder to reduce the risk of damage being caused by an excessively highoperating temperature.

The PMIC 300 comprises an LED driver 320 which, in this example,receives a digital drive signal from the digital core 316 and providesLED drive output signals to six LEDs 321-326 which are configured to becoupled to output pins of the PMIC 300. The LED driver 320 can thusdrive and dim the LEDs 321-326 in up to six independent channels.

The PMIC 300 comprises a first digital to analogue converter (DAC) 327which converts digital signals within the PMIC 300 into an analoguevoltage control signal which is output from the PMIC 300 via an outputpin VDAC0. The first DAC 327 converts a digital control signal generatedby the digital core 316 into an analogue voltage control signal which isoutput via the output pin VDAC0 to control a voltage regulator circuit,such as the boost converter 305. The voltage control signal thuscontrols the voltage regulator circuit to generate a predeterminedvoltage for modulation by the H-bridge circuit to drive the ultrasonictransducer 215 in response to feedback signals which are indicative ofthe operation of the ultrasonic transducer 215.

In this example, the PMIC 300 comprises a second DAC 328 which convertsdigital signals within the PMIC 300 into an analogue signal which isoutput from the PMIC 300 via a second analogue output pin VDAC1.

Embedding the DACs 327, 328 within the same microchip as the othersubsystems of the PMIC 300 allows the DACs 327, 328 to communicate withthe digital core 316 and other components within the PMIC 300 at highspeed with no or minimal communication lag. The DACs 327, 328 provideanalogue outputs which control external feedback loops. For instance,the first DAC 327 provides the control signal VCTL to the boostconverter 305 to control the operation of the boost converter 305. Inother examples, the DACs 327, 328 are configured to provide a drivesignal to a DC-DC buck converter instead of or in addition to the boostconverter 305. Integrating the two independent DAC channels in the PMIC300 enables the PMIC 300 to manipulate the feedback loop of anyregulator used in the hookah device 202 and allows the hookah device 202to regulate the sonication power of the ultrasonic transducer 215 or toset analogue thresholds for absolute maximum current and temperaturesettings of the ultrasonic transducer 215.

The PMIC 300 comprises a serial communication interface which, in thisexample, is an I2C interface which incorporates external I2C address setthrough pins.

The PMIC 300 also comprises various functional blocks which include adigital machine (FSM) to implement the functionality of the microchip.These blocks will be described in more detail below.

Referring now to FIG. 32 of the accompanying drawings, a pulse widthmodulation (PWM) signal generator subsystem 329 is embedded within thePMIC 300. The PWM generator system 329 comprises the oscillator 315, andfrequency divider 330, a multiplexer 331 and a delay locked loop (DLL)332. As will be described below, the PWM generator system 329 is a twophase centre aligned PWM generator.

The frequency divider 330, the multiplexer 331 and the DLL 332 areimplemented in digital logic components (e.g. transistors, logic gates,etc.) within the digital core 316.

In examples of this disclosure, the frequency range which is covered bythe oscillator 315 and respectively by the PWM generator system 329 is50 kHz to 5 MHz or up to 105 MHz. The frequency accuracy of the PWMgenerator system 329 is ±1% and the spread over temperature is ±1%. Inthe IC market today, no IC has an embedded oscillator and two phasecentre aligned PWM generator that can provide a frequency range of 50kHz to 5 MHz or up to 105 MHz.

The oscillator 315 generates a main clock signal (clk_m) with afrequency of 50 kHz to 5 MHz or up to 105 MHz. The main clock clk_m isinput to the frequency divider 330 which divides the frequency of themain clock clk_m by one or more predetermined divisor amounts. In thisexample, the frequency divider 330 divides the frequency of the mainclock clk_m by 2, 4, 8 and 16 and provides the divided frequency clocksas outputs to the multiplexer 331. The multiplexer 331 multiplexes thedivided frequency clocks and provides a divided frequency output to theDLL 332. This signal which is passed to the DLL 332 is a frequencyreference signal which controls the DLL 332 to output signals at adesired frequency. In other examples, the frequency divider 330 and themultiplexer 331 are omitted.

The oscillator 315 also generates two phases; a first phase clock signalPhase 1 and a second phase clock signal Phase 2. The phases of the firstphase clock signal and the second phase clock signal are centre aligned.As illustrated in FIG. 33:

-   -   The first phase clock signal Phase 1 is high for a variable time        of clk_m's positive half-period and low during clk_m's negative        half-period.    -   The second phase clock signal Phase 2 is high for a variable        time of clk_m's negative half-period and low during clk_m's        positive half-period.

Phase 1 and Phase 2 are then sent to the DLL 332 which generates adouble frequency clock signal using the first phase clock signal Phase 1and the second phase clock signal Phase 2. The double frequency clocksignal is double the frequency of the main clock signal clk_m. In thisexample, an “OR” gate within the DLL 332 generates the double frequencyclock signal using the first phase clock signal Phase 1 and the secondphase clock signal Phase 2. This double frequency clock or the dividedfrequency coming from the frequency divider 330 is selected based on atarget frequency selected and then used as reference for the DLL 332.

Within the DLL 332, a signal referred to hereafter as “clock” representsthe main clock clk_m multiplied by 2, while a signal referred tohereafter as “clock_del” is a replica of clock delayed by one period ofthe frequency. Clock and clock_del are passed through a phase frequencydetector. A node Vc is then charged or discharged by a charge-pump basedon the phase error polarity. A control voltage is fed directly tocontrol the delay of every single delay unit within the DLL 332 untilthe total delay of the DLL 332 is exactly one period.

The DLL 332 controls the rising edge of the first phase clock signalPhase 1 and the second phase clock signal Phase 2 to be synchronous withthe rising edge of the double frequency clock signal. The DLL 332adjusts the frequency and the duty cycle of the first phase clock signalPhase 1 and the second phase clock signal Phase 2 in response to arespective frequency reference signal and a duty cycle control signal toproduce a first phase output signal Phase A and a second phase outputsignal Phase B to drive an H-bridge or an inverter to generate an ACdrive signal to drive an ultrasonic transducer.

The PMIC 300 comprises a first phase output signal terminal PHASE_Awhich outputs the first phase output signal Phase A to an H-bridgecircuit and a second phase output signal terminal PHASE_B which outputsthe second phase output signal Phase B to an H-bridge circuit.

In this example, the DLL 332 adjusts the duty cycle of the first phaseclock signal Phase 1 and the second phase clock signal Phase 2 inresponse to the duty cycle control signal by varying the delay of eachdelay line in the DLL 332 response to the duty cycle control signal.

The clock is used at double of its frequency because guarantees betteraccuracy. As shown in FIG. 34, for the purpose of explanation if thefrequency of the main clock clk_m is used (which it is not in examplesof this disclosure), Phase A is synchronous with clock's rising edge R,while Phase B is synchronous with clock's falling edge F. The delay lineof the DLL 332 controls the rising edge R and so, for the falling edgeF, the PWM generator system 329 would need to rely on a perfect matchingof the delay units of the DLL 332 which can be imperfect. However, toremove this error, the PWM generator system 329 uses the doublefrequency clock so that both Phase A and Phase B are synchronous withthe rising edge R of the double frequency clock.

To perform a duty-cycle from 20% to 50% with a 2% step size, the delayline of the DLL 332 comprises 25 delay units, with the output of eachrespective delay unit representing a Phase nth. Eventually the phase ofthe output of the final delay unit will correspond to the input clock.Considering that all delays will be almost the same, a particular dutycycle is obtained with the output of the specific delay unit with simplelogic in the digital core 316.

It is important to take care of the DLL 332 startup as the DLL 332 mightnot be able to lock a period of delay but two or more periods, takingthe DLL 332 to a non-convergence zone. To avoid this issue, a start-upcircuit is implemented in the PWM generator system 329 which allows theDLL 332 to start from a known and deterministic condition. The start-upcircuit furthermore allows the DLL 332 to start with the minimum delay.

In examples of this disclosure, the frequency range covered by the PWMgenerator system 329 is extended and so the delay units in the DLL 332can provide delays of 4 ns (for an oscillator frequency of 5 MHz) to 400ns (for an oscillator frequency of 50 kHz). In order to accommodate forthese differing delays, capacitors Cb are included in the PWM generatorsystem 329, with the capacitor value being selected to provide therequired delay.

The Phase A and Phase B are output from the DLL 332 and passed through adigital 10 to the bridge IC 301 so that the Phase A and Phase B can beused to control the operation of the bridge IC 301.

The battery charging functionality of some examples of the hookah device202 will now be described in more detail. It is, however, to beappreciated that the battery charging functionality may be omitted inother examples in which the hookah device 202 is configure to be poweredby an external power source instead of a battery.

In this example, the battery charging sub-system comprises the chargercircuit 317 which is embedded in the PMIC 300 and controlled by adigital charge controller hosted in the PMIC 300. The charger circuit317 is controlled by the microcontroller 303 via the communication bus302. The battery charging sub-system is able to charge a single celllithium polymer (LiPo) or lithium-ion (Li-ion) battery.

In this example, the battery charging sub-system is able to charge abattery or batteries with a charging current of up to 1 A from a 5Vpower supply (e.g. a USB power supply). One or more of the followingparameters can be programmed through the communication bus 302 (I2Cinterface) to adapt the charge parameters for the battery:

-   -   Charge voltage can be set between 3.9V and 4.3V in 100 mV steps.    -   The charge current can be set between 150 mA and 1000 mA in 50        mA steps.    -   The pre-charge current is 1/10 of the charge current.    -   Pre-charge and fast charge timeouts can be set between 5 and 85        min respectively 20 and 340 min.    -   Optionally an external negative temperature coefficient (NTC)        thermistor can be used to monitor the battery temperature.

In some examples, the battery charging sub-system reports one or more ofthe following events by raising an interrupt to the host microcontroller303:

-   -   Battery detected    -   Battery is being charged    -   Battery is fully charged    -   Battery is not present    -   Charge timeout reached    -   Charging supply is below the undervoltage limit

The main advantage of having the charger circuit 317 embedded in thePMIC 300, is that it allows all the programming options and eventindications listed to be implemented within the PMIC 300 whichguarantees the safe operation of the battery charging sub-system.Furthermore, a significant manufacturing cost and PCB space saving canbe accomplished compared with conventional mist inhaler devices whichcomprise discrete components of a charging system mounted separately ona PCB. The charger circuit 317 also allows for highly versatile settingof charge current and voltage, different fault timeouts and numerousevent flags for detailed status analysis.

The analogue to digital converter (ADC) 318 will now be described inmore detail. The inventors had to overcome significant technicalchallenges to integrate the ADC 318 within the PMIC 300 with the highspeed oscillator 315. Moreover, integrating the ADC 318 within the PMIC300 goes against the conventional approach in the art which relies onusing one of the many discrete ADC devices that are available in the ICmarket.

In this example, the ADC 318 samples at least one parameter within theultrasonic transducer driver chip (PMIC 300) at a sampling rate which isequal to the frequency of the main clock signal clk_m. In this example,the ADC 318 is a 10 bit analogue to digital converter which is able tounload digital sampling from the microprocessor 303 to save theresources of the microprocessor 303. Integrating the ADC 318 within thePMIC 300 also avoids the need to use an I2C bus that would otherwiseslow down the sampling ability of the ADC (a conventional device relieson an I2C bus to communicate data between a dedicated discrete ADC and amicrocontroller at a limited clock speed of typically up to 400 kHz).

In examples of this disclosure, one or more of the following parameterscan be sampled sequentially by the ADC 318:

-   -   i. An rms current signal which is received at the ultrasonic        transducer driver chip (PMIC 300) from an external inverter        circuit which is driving an ultrasonic transducer. In this is        example, this parameter is a root mean square (rms) current        reported by the bridge IC 301. Sensing the rms current is        important to implementing the feedback loop used for driving the        ultrasound transducer 215. The ADC 318 is able to sense the rms        current directly from the bridge IC 301 via a signal with        minimal or no lag since the ADC 318 does not rely on this        information being transmitted via an I2C bus. This provides a        significant speed and accuracy benefit over conventional devices        which are constrained by the comparatively low speeds of an I2C        bus.    -   ii. The voltage of a battery connected to the PMIC 300.    -   iii. The voltage of a charger connected to the PMIC 300.    -   iv. A temperature signal, such as a temperature signal which is        indicative of the PMIC 300 chip temperature. As described above,        this temperature can be measured very accurately due to the        temperature sensor 314 being embedded in the same IC as the        oscillator 315. For example, if the PMIC 300 temperature goes        up, the current, frequency and PWM are regulated by the PMIC 300        to control the transducer oscillation which in turn controls the        temperature.    -   v. Two external pins.    -   vi. External NTC temperature sensor to monitor battery pack        temperature.

In some examples, the ADC 318 samples one or more of the above-mentionedsources sequentially, for instance in a round robin scheme. The ADC 318samples the sources at high speed, such as the speed of the oscillator315 which may be up to 5 MHz or up to 105 MHz.

In some examples, the device 202 is configured so that a user or themanufacturer of the device can specify how many samples shall be takenfrom each source for averaging. For instance, a user can configure thesystem to take 512 samples from the rms current input, 64 samples fromthe battery voltage, 64 from the charger input voltage, 32 samples fromthe external pins and 8 from the NTC pin. Furthermore, the user can alsospecify if one of the above-mentioned sources shall be skipped. In someexamples, the hookah device 202 is configured by a user via an externalcomputing device which communicates wirelessly with the hookah device202 (e.g. via BLE).

In some examples, for each source the user can specify two digitalthresholds which divide the full range into a plurality of zones, suchas 3 zones. Subsequently the user can set the system to release aninterrupt when the sampled value changes zones e.g. from a zone 2 to azone 3.

No conventional IC available in the market today can perform the abovefeatures of the PMIC 300. Sampling with such flexibility and granularityis paramount when driving an ultrasound transducer.

In this example, the PMIC 300 comprises an 8 bit general purpose digitalinput output port (GPIO). Each port can be configured as digital inputand digital output. Some of the ports have an analogue input function,as shown in the table in FIG. 35.

The GPIO7-GPIO5 ports of the PMIC 300 can be used to set the device'saddress on the communication (I2C) bus 302. Subsequently eight identicaldevices can be used on the same I2C bus. This is a unique feature in theIC industry since it allows eight identical devices to be used on thesame I2C bus without any conflicting addresses. This is implemented byeach device reading the state of GPIO7-GPIO5 during the first 100 μsafter the startup of the PMIC 300 and storing that portion of theaddress internally in the PMIC 300. After the PMIC 300 has been startedup the GPIOs can be used for any other purpose.

As described above, the PMIC 300 comprises a six channel LED driver 320.In this example the LED driver 320 comprises N-Channel Metal-OxideSemiconductor (NMOS) current sources which are 5V tolerant. The LEDdriver 320 is configured to set the LED current in four discrete levels;5 mA, 10 mA, 15 mA and 20 mA. The LED driver 320 is configured to dimeach LED channel with a 12 bit PWM signal either with or without gammacorrection. The LED driver 320 is configured to vary the PWM frequencyfrom 300 Hz to 1.5 KHz. This feature is unique in the field ofultrasonic mist inhaler devices as the functionality is embedded as asub-system of the PMIC 300.

In this example, the PMIC 300 comprises two independent 6 Bit Digital toAnalog Converters (DAC) 327, 328 which are incorporated into the PMIC300. The purpose of the DACs 327, 328 is to output an analogue voltageto manipulate the feedback path of an external regulator (e.g. the DC-DCBoost converter 305 a Buck converter or a LDO). Furthermore, in someexamples, the DACs 327, 328 can also be used to dynamically adjust theover current shutdown level of the bridge IC 301, as described below.

The output voltage of each DAC 327, 328 is programmable between 0V and1.5V or between 0V and V_battery (Vbat). In this example, the control ofthe DAC output voltage is done via I2C commands. Having two DACincorporated in the PMIC 300 is unique and will allow the dynamicmonitoring control of the current. If either DAC 327, 328 was anexternal chip, the speed would fall under the same restrictions of speedlimitations due to the I2C protocol. The active power monitoringarrangement of the device 202 works with optimum efficiency if all theseembedded features are in the PMIC. Had they been external components,the active power monitoring arrangement would be totally inefficient.

Referring now to FIG. 36 of the accompanying drawings, the bridge IC 301is a microchip which comprises an embedded power switching circuit 333.In this example, the power switching circuit 333 is an H-bridge 334which is shown in FIG. 37 and which is described in detail below. It is,however, to be appreciated that the bridge IC 301 of other examples mayincorporate an alternative power switching circuit to the H-bridge 334,provided that the power switching circuit performs an equivalentfunction for generating an AC drive signal to drive the ultrasonictransducer 215.

The bridge IC 301 comprises a first phase terminal PHASE A whichreceives a first phase output signal Phase A from the PWM signalgenerator subsystem of the PMIC 300. The bridge IC 301 also comprises asecond phase terminal PHASE B which receives a second phase outputsignal Phase B from the PWM signal generator subsystem of the PMIC 300.

The bridge IC 301 comprises a current sensing circuit 335 which sensescurrent flow in the H-bridge 334 directly and provides an RMS currentoutput signal via the RMS_CURR pin of the bridge IC 301. The currentsensing circuit 335 is configured for over current monitoring, to detectwhen the current flowing in the H-bridge 334 is above a predeterminedthreshold. The integration of the power switching circuit 333 comprisingthe H-bridge 334 and the current sensing circuit 335 all within the sameembedded circuit of the bridge IC 301 is a unique combination in the ICmarket. At present, no other integrated circuit in the IC marketcomprises an H-bridge with embedded circuitry for sensing the RMScurrent flowing through the H-bridge.

The bridge IC 301 comprises a temperature sensor 336 which includes overtemperature monitoring. The temperature sensor 336 is configured to shutdown the bridge IC 301 or disable at least part of the bridge IC 336 inthe event that the temperature sensor 336 detects that the bridge IC 301is operating at a temperature above a predetermined threshold. Thetemperature sensor 336 therefore provides an integrated safety functionwhich prevents damage to the bridge IC 301 or other components withinthe hookah device 202 in the event that the bridge IC 301 operates at anexcessively high temperature.

The bridge IC 301 comprises a digital state machine 337 which isintegrally connected to the power switching circuit 333. The digitalstate machine 337 receives the phase A and phase B signals from the PMIC300 and an ENABLE signal, for instance from the microcontroller 303. Thedigital state machine 337 generates timing signals based on the firstphase output signal Phase A and the second phase output signal Phase B.

The digital state machine 337 outputs timing signals corresponding tothe phase A and phase B signals as well as a BRIDGE_PR and BRIDGE_ENsignals to the power switching circuit 333 in order to control the powerswitching circuit 333. The digital state machine 337 thus outputs thetiming signals to the switches T₁-T₄ of the H-bridge circuit 334 tocontrol the switches T₁-T₄ to turn on and off in a sequence such thatthe H-bridge circuit outputs an AC drive signal for driving a resonantcircuit, such as the ultrasonic transducer 215.

As described in more detail below, the switching sequence comprises afree-float period in which the first switch T₁ and the second switch T₂are turned off and the third switch T₃ and the fourth switch T₄ areturned on in order to dissipate energy stored by the resonant circuit(the ultrasonic transducer 215).

The bridge IC 301 comprises a test controller 338 which enables thebridge IC 301 to be tested to determine whether the embedded componentswithin the bridge IC 301 are operating correctly. The test controller338 is coupled to TEST_DATA, TEST_CLK and TEST_LOAD pins so that thebridge IC 301 can be connected to an external control device which feedsdata into and out from the bridge IC 301 to test the operation of thebridge IC 301. The bridge IC 301 also comprises a TEST BUS which enablesthe digital communication bus within the bridge IC 301 to be tested viaa TST_PAD pin.

The bridge IC 301 comprises a power on reset circuit (POR) 339 whichcontrols the startup operation of the bridge IC 301. The POR 339 ensuresthat the bridge IC 301 starts up properly only if the supply voltage iswithin a predetermined range. If the power supply voltage is outside ofthe predetermined range, for instance if the power supply voltage is toohigh, the POR 339 delays the startup of the bridge IC 301 until thesupply voltage is within the predetermined range.

The bridge IC 301 comprises a reference block (BG) 340 which provides aprecise reference voltage for use by the other subsystems of the bridgeIC 301.

The bridge IC 301 comprises a current reference 341 which provides aprecise current to the power switching circuit 333 and/or othersubsystems within the bridge IC 301, such as the current sensor 335.

The temperature sensor 336 monitors the temperature of the silicon ofthe bridge IC 301 continuously. If the temperature exceeds thepredetermined temperature threshold, the power switching circuit 333 isswitched off automatically. In addition, the over temperature may bereported to an external host to inform the external host that an overtemperature event has occurred.

The digital state machine (FSM) 337 generates the timing signals for thepower switching circuit 333 which, in this example, are timing signalsfor controlling the H-bridge 334.

The bridge IC 301 comprises comparators 342,343 which compare signalsfrom the various subsystems of the bridge IC 301 with the voltage andcurrent references 340,341 and provide reference output signals via thepins of the bridge IC 301.

Referring again to FIG. 37 of the accompanying drawings, the H-bridge334 of this example comprises four switches in the form of NMOS fieldeffect transistors (FET) switches on both sides of the H-bridge 334. TheH-bridge 334 comprises four switches or transistors T₁-T₄ which areconnected in an H-bridge configuration, with each transistor T₁-T₄ beingdriven by a respective logic input A-D. The transistors T₁-T₄ areconfigured to be driven by a bootstrap voltage which is generatedinternally with two external capacitors Cb which are connected asillustrated in FIG. 37.

The H-bridge 334 comprises various power inputs and outputs which areconnected to the respective pins of the bridge IC 301. The H-bridge 334receives the programmable voltage VBOOST which is output from the boostconverter 305 via a first power supply terminal, labelled VBOOST in FIG.37. The H-bridge 334 comprises a second power supply terminal, labelledVSS_P in FIG. 37.

The H-bridge 334 comprises outputs OUTP, OUTN which are configured toconnect to respective terminals of the ultrasonic transducer 215 so thatthe AC drive signal output from the H-bridge 334 can drive theultrasonic transducer 215.

The switching of the four switches or transistors T₁-T₄ is controlled byswitching signals from the digital state machine 337 via the logic inputA-D. It is to be appreciated that, while FIG. 37 shows four transistorsT₁-T₄, in other examples, the H-bridge 334 incorporates a larger numberof transistors or other switching components to implement thefunctionality of the H-bridge.

In this example, the H-bridge 334 operates at a switching power of 22 Wto 37 W in order to deliver an AC drive signal with sufficient power todrive the ultrasonic transducer 215 to generate mist optimally. Thevoltage which is switched by the H-bridge 334 of this example is ±15 V.In other examples, the voltage is ±20 V.

In this example, the H-bridge 334 switches at a frequency of 3 MHz to 5MHz or up to 105 MHz. This is a high switching speed compared withconventional integrated circuit H-bridges which are available in the ICmarket. For instance, a conventional integrated circuit H-bridgeavailable in the IC market today is configured to operate at a maximumfrequency of only 2 MHz. Aside from the bridge IC 301 described herein,no conventional integrated circuit H-bridge available in the IC marketis able to operate at a power of 22 V to 37 V at a frequency of up to 5MHz, let alone up to 105 MHz.

Referring now to FIG. 38 of the accompanying drawings, the currentsensor 335 comprises positive and negative current sense resistorsRshuntP, RshuntN which are connected in series with the respective highand low sides of the H-bridge 334, as shown in FIG. 37. The currentsense resistors RshuntP, RshuntN are low value resistors which, in thisexample, are 0.1Ω. The current sensor 335 comprises a first voltagesensor in the form of a first operational amplifier 344 which measuresthe voltage drop across the first current sensor resistor RshuntP and asecond voltage sensor in the form of a second operational amplifier 345which measures the voltage drop across the second current sensorresistor RshuntN. In this example, the gain of each operationalamplifier 344, 345 is 2V/V. The output of each operational amplifier344, 345 is, in this example, 1 mA/V. The current sensor 335 comprises apull down resistor R_(cs) which, in this example, is 2 kΩ. The outputsof the operational amplifiers 344, 345 provide an output CSout whichpasses through a low pass filter 346 which removes transients in thesignal CSout. An output Vout of the low pass filter 346 is the outputsignal of the current sensor 335.

The current sensor 335 thus measures the AC current flowing through theH-bridge 334 and respectively through the ultrasonic transducer 215. Thecurrent sensor 335 translates the AC current into an equivalent RMSoutput voltage (Vout) relative to ground. The current sensor 335 hashigh bandwidth capability since the H-bridge 334 can be operated at afrequency of up to 5 MHz or, in some examples, up to 105 MHz. The outputVout of the current sensor 335 reports a positive voltage which isequivalent to the measured AC rms current flowing through the ultrasonictransducer 215. The output voltage Vout of the current sensor 335 is, inthis example, fed back to the control circuitry within the bridge IC 301to enable the bridge IC 301 to shut down the H-bridge 334 in the eventthat the current flowing through the H-bridge 334 and hence through thetransducer 215 is in excess of a predetermined threshold. In addition,the over current threshold event is reported to the first comparator 342in the bridge IC 301 so that the bridge IC 301 can report the overcurrent event via the OVC_TRIGG pin of the bridge IC 301.

Referring now to FIG. 39 of the accompanying drawings, the control ofthe H-bridge 334 will now be described also with reference to theequivalent piezoelectric model of the ultrasonic transducer 215.

To develop a positive voltage across the outputs OUTP, OUTN of theH-bridge 334 as indicated by V_out in FIG. 39 (note the direction of thearrow) the switching sequence of the transistors T₁-T₄ via the inputsA-D is as follows:

-   -   1. Positive output voltage across the ultrasonic transducer 215:        A-ON, B-OFF, C-OFF, D-ON    -   2. Transition from positive output voltage to zero: A-OFF,        B-OFF, C-OFF, D-ON. During this transition, C is switched off        first to minimise or avoid power loss by minimising or avoiding        current flowing through A and C if there is a switching error or        delay in A.    -   3. Zero output voltage: A-OFF, B-OFF, C-ON, D-ON. During this        zero output voltage phase, the terminals of the outputs OUTP,        OUTN of the H-bridge 334 are grounded by the C and D switches        which remain on. This dissipates the energy stored by the        capacitors in the equivalent circuit of the ultrasonic        transducer, which minimises the voltage overshoot in the        switching waveform voltage which is applied to the ultrasonic        transducer.    -   4. Transition from zero to negative output voltage: A-OFF,        B-OFF, C-ON, D-OFF.    -   5. Negative output voltage across the ultrasonic transducer 215:        A-OFF, B-ON, C-ON, D-OFF

At high frequencies of up to 5 MHz or even up to 105 MHz, it will beappreciated that the time for each part of the switching sequence isvery short and in the order of nanoseconds or picoseconds. For instance,at a switching frequency of 6 MHz, each part of the switching sequenceoccurs in approximately 80 ns.

A graph showing the output voltage OUTP, OUTN of the H-bridge 334according to the above switching sequence is shown in FIG. 40 of theaccompanying drawings. The zero output voltage portion of the switchingsequence is included to accommodate for the energy stored by theultrasonic transducer 215 (e.g. the energy stored by the capacitors inthe equivalent circuit of the ultrasonic transducer). As describedabove, this minimises the voltage overshoot in the switching waveformvoltage which is applied to the ultrasonic transducer and henceminimises unnecessary power dissipation and heating in the ultrasonictransducer.

Minimising or removing voltage overshoot also reduces the risk of damageto transistors in the bridge IC 301 by preventing the transistors frombeing subject to voltages in excess of their rated voltage. Furthermore,the minimisation or removal of the voltage overshoot enables the bridgeIC 301 to drive the ultrasonic transducer accurately in a way whichminimises disruption to the current sense feedback loop describedherein. Consequently, the bridge IC 301 is able to drive the ultrasonictransducer at a high power of 22 W to 50 W or even as high as 70 W at ahigh frequency of up to 5 MHz or even up to 105 MHz.

The bridge IC 301 of this example is configured to be controlled by thePMIC 300 to operate in two different modes, referred to herein as aforced mode and a native frequency mode. These two modes of operationare novel over existing bridge ICs. In particular, the native frequencymode is a major innovation which offers substantial benefits in theaccuracy and efficiency of driving an ultrasonic transducer as comparedwith conventional devices.

Forced Frequency Mode (FFM)

In the forced frequency mode the H-bridge 334 is controlled in thesequence described above but at a user selectable frequency. As aconsequence, the H-bridge transistors T₁-T₄ are controlled in a forcedway irrespective of the inherent resonant frequency of the ultrasonictransducer 215 to switch the output voltage across the ultrasonictransducer 215. The forced frequency mode therefore allows the H-bridge334 to drive the ultrasonic transducer 215, which has a resonantfrequency f1, at different frequency f2.

Driving an ultrasonic transducer at a frequency which is different fromits resonant frequency may be appropriate in order to adapt theoperation to different applications. For example, it may be appropriateto drive an ultrasonic transducer at a frequency which is slightly offthe resonance frequency (for mechanical reasons to prevent mechanicaldamage to the transducer). Alternatively, it may be appropriate to drivean ultrasonic transducer at a low frequency but the ultrasonictransducer has, because of its size, a different native resonancefrequency.

The hookah device 202 controls the bridge IC 301 to drive the ultrasonictransducer 215 in the forced frequency mode in response to theconfiguration of the hookah device 202 for a particular application or aparticular ultrasonic transducer. For instance, the hookah device 202may be configured to operate in the forced frequency mode when the mistinhaler device 200 is being used for a particular application, such asgenerating a mist from a liquid of a particular viscosity containing adrug for delivery to a user.

Native Frequency Mode (NFM)

The following native frequency mode of operation is a significantdevelopment and provides benefits in improved accuracy and efficiencyover conventional ultrasonic drivers that are available on the IC markettoday.

The native frequency mode of operation follows the same switchingsequence as described above but the timing of the zero output portion ofthe sequence is adjusted to minimise or avoid problems that can occurdue to current spikes in the forced frequency mode operation. Thesecurrent spikes occur when the voltage across the ultrasonic transducer215 is switched to its opposite voltage polarity. An ultrasonictransducer which comprises a piezoelectric crystal has an electricalequivalent circuit which incorporates a parallel connected capacitor(e.g. see the piezo model in FIG. 39). If the voltage across theultrasonic transducer is hard-switched from a positive voltage to anegative voltage, due to the high dV/dt there can be a large currentflow current flow as the energy stored in the capacitor dissipates.

The native frequency mode avoids hard switching the voltage across theultrasonic transducer 215 from a positive voltage to a negative voltage(and vice versa). Instead, prior to applying the reversed voltage, theultrasonic transducer 215 (piezoelectric crystal) is left free-floatingwith zero voltage applied across its terminals for a free-float period.The PMIC 300 sets the drive frequency of the bridge IC 301 such that thebridge 334 sets the free-float period such that current flow inside theultrasonic transducer 215 (due to the energy stored within thepiezoelectric crystal) reverses the voltage across the terminals of theultrasonic transducer 215 during the free-float period.

Consequently, when the H-bridge 334 applies the negative voltage at theterminals of the ultrasonic transducer 215 the ultrasonic transducer 215(the capacitor in the equivalent circuit) has already been reversecharged and no current spikes occur because there is no high dV/dt.

It is, however, to be appreciated that it takes time for the chargewithin the ultrasonic transducer 215 (piezoelectric crystal) to build upwhen the ultrasonic transducer 215 is first activated. Therefore, theideal situation in which the energy within the ultrasonic transducer 215is to reverse the voltage during the free-float period occurs only afterthe oscillation inside the ultrasonic transducer 215 has built up thecharge. To accommodate for this, when the bridge IC 301 activates theultrasonic transducer 215 for the first time, the PMIC 300 controls thepower delivered through the H-bridge 334 to the ultrasonic transducer215 to a first value which is a low value (e.g. 5 V). The PMIC 300 thencontrols the power delivered through the H-bridge 334 to the ultrasonictransducer 215 to increase over a period of time to a second value (e.g.15 V) which is higher than the first value in order to build up theenergy stored within the ultrasonic transducer 215. Current spikes stilloccur during this ramp of the oscillation until the current inside theultrasonic transducer 215 developed sufficiently. However, by using alow first voltage at start up those current spikes are kept sufficientlylow to minimise the impact on the operation of the ultrasonic transducer215.

In order to implement the native frequency mode, the hookah device 202controls the frequency of the oscillator 315 and the duty cycle (ratioof turn-on time to free-float time) of the AC drive signal output fromthe H-bridge 334 with high precision. In this example, the hookah device202 performs three control loops to regulate the oscillator frequencyand the duty cycle such that the voltage reversal at the terminals ofthe ultrasonic transducer 215 is as precise as possible and currentspikes are minimised or avoided as far as possible. The precise controlof the oscillator and the duty cycle using the control loops is asignificant advance in the field of IC ultrasonic drivers.

During the native frequency mode of operation, the current sensor 335senses the current flowing through the ultrasonic transducer 215(resonant circuit) during the free-float period. The digital statemachine 337 adapts the timing signals to switch on either the firstswitch T₁ or the second switch T₂ when the current sensor 335 sensesthat the current flowing through the ultrasonic transducer 215 (resonantcircuit) during the free-float period is zero.

FIG. 41 of the accompanying drawings shows the oscillator voltagewaveform 347 (V(osc)), a switching waveform 348 resulting from theturn-on and turn-off the left hand side high switch T₁ of the H-bridge334 and a switching waveform 349 resulting from the turn-on and turn-offthe right hand side high switch T₂ of the H-bridge 334. For anintervening free-float period 350, both high switches T₁, T₂ of theH-bridge 334 are turned off (free-floating phase). The duration of thefree-float period 350 is controlled by the magnitude of the free-floatcontrol voltage 351 (Vphioff).

FIG. 42 of the accompanying drawings shows the voltage waveform 352 at afirst terminal of the ultrasonic transducer 215 (the voltage waveform isreversed at the second terminal of the ultrasonic transducer 215) andthe piezo current 353 flowing through the ultrasonic transducer 215. Thepiezo current 353 represents an (almost) ideal sinusoidal waveform (thisis never possible in the forced frequency mode or in any bridge in theIC market).

Before the sinusoidal wave of the piezo current 353 reaches zero, theleft hand side high switch T₁ of the H-bridge 334 is turned off (here,the switch T₁ is turned off when the piezo current 353 is approximately6 A). The remaining piezo current 353 which flows within the ultrasonictransducer 215 due to the energy stored in the ultrasonic transducer 215(the capacitor of the piezo equivalent circuit) is responsible for thevoltage reversal during the free-float period 350. The piezo current 353decays to zero during the free-float period 350 and into negativecurrent flow domain thereafter. The terminal voltage at the ultrasonictransducer 215 drops from the supply voltage (in this case 19 V) to lessthan 2 V and the drop comes to a stop when the piezo current 353 reacheszero. This is the perfect time to turn on the low-side switch T₃ of theH-bridge 334 in order to minimise or avoid a current spike.

Compared to the forced frequency mode described above, the nativefrequency mode has at least three advantages:

-   -   1. The current spike associated with hard switching of the        package capacitor is significantly reduced or avoided        completely.    -   2. Power loss due to hard switching is almost eliminated.    -   3. Frequency is regulated by the control loops and will be kept        close to the resonance of the piezo crystal (i.e. the native        resonance frequency of the piezo crystal).

In the case of the frequency regulation by the control loops (advantage3 above), the PMIC 300 starts by controlling the bridge IC 301 to drivethe ultrasonic transducer 215 at a frequency above the resonance of thepiezo crystal. The PMIC 300 then controls the bridge IC 301 to that thefrequency of the AC drive signal decays/reduces during start up. As soonas the frequency approaches resonance frequency of the piezo crystal,the piezo current will develop/increase rapidly. Once the piezo currentis high enough to cause the desired voltage reversal, the frequencydecay/reduction is stopped by the PMIC 300. The control loops of thePMIC 300 then take over the regulation of frequency and duty cycle ofthe AC drive signal.

In the forced frequency mode, the power delivered to the ultrasonictransducer 215 is controlled through the duty cycle and/or a frequencyshift and/or by varying the supply voltage. However, in this example inthe native frequency mode the power delivered to the ultrasonictransducer 215 controlled only through the supply voltage.

In this example, during a setup phase of operation of the hookah device,the bridge IC 301 is configured to measure the length of time taken forthe current flowing through the ultrasonic transducer 215 (resonantcircuit) to fall to zero when the first switch T₁ and the second switchT₂ are turned off and the third switch T₃ and the fourth switch T₄ areturned on. The bridge IC 301 then sets the length of time of thefree-float period to be equal to the measured length of time.

Referring now to FIG. 43 of the accompanying drawings, the PMIC 300 andthe bridge IC 301 of this example are designed to work together as acompanion chip set. The PMIC 300 and the bridge IC 301 are connectedtogether electrically for communication with one another. In thisexample, there are interconnections between the PMIC 300 and the bridgeIC 301 which enable the following two categories of communication:

-   -   1. control signals    -   2. feedback signals

The connections between the PHASE_A and PHASE_B pins of the PMIC 300 andthe bridge IC 301 carry the PWM modulated control signals which drivethe H-bridge 334.

The connection between the EN_BR pins of the PMIC 300 and the bridge IC301 carries the EN_BR control signal which triggers the start of theH-bridge 334. The timing between the PHASE_A, PHASE_B and EN_BR controlsignals is important and handled by the digital bridge control of thePMIC 300.

The connections between the CS, OC and OT pins of the PMIC 300 and thebridge IC 301 carry CS (current sense), OC (over current) and OT (overtemperature) feedback signals from the bridge IC 301 back to the PMIC300. Most notably, the CS (current sense) feedback signal comprises avoltage equivalent to the rms current flowing through the ultrasonictransducer 215 which is measured by the current sensor 335 of the bridgeIC 301.

The OC (over current) and OT (over temperature) feedback signals aredigital signals indicating that either an over current or an overvoltage event has been detected by the bridge IC 301. In this example,the thresholds for the over current and over temperature are set with anexternal resistor. Alternatively, the thresholds can also be dynamicallyset in response to signals passed to the OC_REF pin of the bridge IC 301from one of the two DAC channels VDAC0, VDAC1 from the PMIC 300.

In this example, the design of the PMIC 300 and the bridge IC 301 allowthe pins of these two integrated circuits to be connected directly toone another (e.g. via copper tracks on a PCB) so that there is minimalor no lag in the communication of signals between the PMIC 300 and thebridge IC 301. This provides a significant speed advantage overconventional bridges in the IC market which are typically controlled bysignals via a digital communications bus. For example, a standard I2Cbus is clocked at only 400 kHz, which is too slow for communicating datasampled at the high clock speeds of up to 5 MHz of examples of thisdisclosure.

While examples of this disclosure have been described above in relationto the microchip hardware, it is to be appreciated that other examplesof this disclosure comprise a method of operating the components andsubsystems of each microchip to perform the functions described herein.For instance, the methods of operating the PMIC 300 and the bridge IC301 in either the forced frequency mode or the native frequency mode.

Referring now to FIG. 44 of the accompanying drawings, the OTP IC 242comprises a power on reset circuit (POR) 354, a bandgap reference (BG)355, a cap-less low dropout regulator (LDO) 356, a communication (e.g.I2C) interface 357, a one-time programmable memory bank (eFuse) 358, anoscillator 359 and a general purpose input-output interface 360. The OTPIC 242 also comprises a digital core 361 which includes a cryptographicauthenticator. In this example, the cryptographic authenticator uses theElliptic Curve Digital Signature Algorithm (ECDSA) forencrypting/decrypting data stored within the OTP IC 242 as well as datatransmitted to and from the OTP IC 242.

The POR 354 ensures that the OTP IC 242 starts up properly only if thesupply voltage is within a predetermined range. If the supply voltage isoutside the predetermined range, the POR 354 resets the OTP IC 242 andwaits until the supply voltage is within the predetermined range.

The BG 355 provides precise reference voltages and currents to the LDO356 and to the oscillator 359. The LDO 356 supplies the digital core361, the communication interface 357 and the eFuse memory bank 358.

The OTP IC 242 is configured to operate in at least the following modes:

-   -   Fuse Programming (Fusing): During efuse programming (programming        of the one time programmable memory) a high current is required        to burn the relevant fuses within the eFuse memory bank 358. In        this mode higher bias currents are provided to maintain gain and        bandwidth of the regulation loop.    -   Fuse Reading: In this mode a medium level current is required to        maintain efuse reading within the eFuse memory bank 358. This        mode is executed during the startup of the OTP IC 242 to        transfer the content of the fuses to shadow registers. In this        mode the gain and bandwidth of the regulation loop is set to a        lower value than in the Fusing Mode.    -   Normal Operation: In this mode the LDO 356 is driven in a very        low bias current condition to operate the OTP IC 242 with low        power so that the OTP IC 242 consumes as little power as        possible.

The oscillator 359 provides the required clock for the digitalcore/engine 361 during testing (SCAN Test), during fusing and duringnormal operation. The oscillator 359 is trimmed to cope with the stricttiming requirements during the fusing mode.

In this example, the communication interface 357 is compliant with theFM+ specification of the I2C standard but it also complies with slow andfast mode. The OTP IC 242 uses the communication interface 357 tocommunicate with the hookah device 202 (the Host) for data and keyexchange.

The digital core 361 implements the control and communicationfunctionality of the OTP IC 242. The cryptographic authenticator of thedigital core 361 enables the OTP IC 242 to authenticate itself (e.g.using ECDSA encrypted messages) with the hookah device 202 (e.g. for aparticular application) to ensure that the OTP IC 242 is genuine andthat the OTP IC 242 is authorised to connect to the hookah device 202.

With reference to FIG. 45 of the accompanying drawings, the OTP IC 242performs the following PKI procedure in order to authenticate the OTP IC242 for use with a Host (e.g. the hookah device 202):

-   -   1. Verify Signer Public Key: The Host requests the Manufacturing        Public key and Certificate. The Host verifies the certificate        with the Authority Public key.    -   2. Verify Device Public Key: If the verification is successful,        the Host requests the Device Public key and Certificate. The        Host verifies the certificate with the Manufacturing Public key.    -   3. Challenge—Response: If the verification is successful, the        Host creates a random number challenge and sends it to the        Device. The End Product signs the random number challenge with        the Device Private key.    -   4. The signature is sent back to the Host for verification using        the Device Public key.

If all steps of the authentication procedure complete successfully thenthe Chain of Trust has been verified back to the Root of Trust and theOTP IC 242 is successfully authenticated for use with the Host. However,if any of the steps of the authentication procedure fail then the OTP IC242 is not authenticated for use with the Host and use of the deviceincorporating the OTP IC 242 is restricted or prevented.

FIGS. 46 to 48 illustrate how air flows through the mist generatordevice 201 during operation.

The sonication of the liquid drug (e.g. nicotine) transforms it intomist (aerosolization). However, this mist would settle over theultrasonic transducer 215 unless enough ambient air is available toreplace the rising aerosol. In the sonication chamber 219, there is arequirement for a continuous supply of air as mist (aerosol) isgenerated and pulled out through the mist outlet port 208. To cater tothis requirement, an airflow channel is provided. In this arrangementthe airflow channel has an average cross-sectional area of 11.5 mm²,which is calculated and designed into the sonication chamber 219 basedon the negative air pressure from an average user. This also controlsthe mist-to-air ratio of the inhaled aerosol, controlling the amount ofdrug delivered to the user.

Based on design requirements, the air flow channel is routed such thatit initiates from the bottom of the sonication chamber 219. The openingat the bottom of the aerosol chamber aligns with and is tightly adjacentto the opening to an airflow bridge in the device. The air flow channelruns vertically upwards along the reservoir and continues until thecenter of the sonication chamber (concentric with the ultrasonictransducer 215). Here, it turns 90° inwards. The flow path thencontinues on until approximately 1.5 mm from the ultrasonic transducer215. This routing ensures maximized ambient air supplied directly in thedirection of the atomization surface of the ultrasonic transducer 215.The airflows through the channel, towards the transducer, collects thegenerated mist as it travels out through the mist outlet port 208.

Referring now to FIGS. 49 and 50 of the accompanying drawings, a hookahdevice 202 of some arrangements is configured to releasably attach to anexisting hookah 246. The hookah device 202 attaches to the stem 247 inplace of a conventional hookah head which would otherwise house thetobacco and the charcoal (or electronic heating element).

The hookah 246 comprises a water chamber and an elongate stem 247 havinga first end which is attached to the water chamber. The stem 247comprises a mist flow path which extends from a second end of the stem247, through the stem 247, to the first end and into the water chamber.

In this arrangement, the hookah device 202 is releasably attached to thesecond end of the stem 247 of the hookah 246. However, in otherarrangements the hookah device 202 is not designed to be removable andis instead fixed to or formed integrally with the stem 247 of the hookah246.

Referring to FIGS. 51-59 of the accompanying drawings, the hookah device202 comprises a housing 248 which incorporates a base 249 and a cover250 which are attached or releasably attached to one another. In thisarrangement, the housing 248 is cylindrical and generally disk-shaped.

In this arrangement, the cover 250 is provided with a plurality of airinlets 251 to allow air to be drawn into the hookah device 202. The base249 is provided with a hookah outlet port 252 to allow air and mist toflow out from the hookah device 202 and into the hookah 246. Thediameter of the hookah outlet port 252 is sufficient to allow a user todraw air quickly through the hookah device 202 and through the hookah246 to generate bubbles of mist which travel through the water in thehookah 246.

In this arrangement, the hookah outlet port 252 is a circular aperturewhich receives the end of the stem 247 of the hookah 246. The hookahdevice 202 is supported on the stem 247 of the hookah 246 with agenerally gas-tight seal being formed between the hookah device 202 andthe stem 247.

In this arrangement, the hookah device 202 is a self-contained devicewith the electronic components and mist generator devices containinge-liquid being housed within the housing 248.

In this arrangement, the hookah device 202 comprises an upper supportplate 253, a middle support plate 254 and a lower support plate 255which are stacked on top of one another. The support plates 253-255support a plurality of mist generator devices 201 within the hookahdevice 202. Each mist generator device is a mist generator device 201 asdescribed in this disclosure. In this arrangement, the mist generatordevices 201 a releasably attached to the hookah device 202 so that themist generator devices 201 can be replaced when empty (i.e. when thee-liquid is partially or completely depleted).

In this arrangement, the hookah device 202 comprises four mist generatordevices 201 which are controlled by the microcontroller 303 of thehookah device 202 (via each respective PMIC 300 and bridge IC 301). Inother arrangements, the hookah device 202 comprises a plurality of mistgenerator devices 201, such as at least two mist generator devices 201or up to eight mist generator devices 201.

The hookah device 202 is provided with first contact terminals 259 whichestablish and electrical connection between the controller of the hookahdevice 202 and the electrical contacts 232 and 233 of each mistgenerator device 201. The hookah device 202 is provided with secondcontact terminals 260 which establish and electrical connection betweenthe controller of the hookah device 202 and the electrical contacts 241on the OTP PCB of each mist generator device 201.

In this arrangement, the hookah device 202 comprises an upper printedcircuit board (PCB) 256 which is positioned on top of the upper supportplate 253 and a middle PCB 257 which is positioned between the middlesupport plate 254 and the lower support plate 255. A lower PCB 258 ispositioned beneath the lower support plate 255. The PCBs 256-258 carrythe electronic components which make up a driver device of the hookahdevice 202. The PCBs 256-258 are coupled electrically to one another toallow the electronic components on each PCB 256-258 to communicate withone another.

While there are three PCBs 256-258 in this arrangement, otherarrangements comprise only one PCB or a plurality of PCBs which performthe same functions of the driver device of the hookah device 202.

In this arrangement, the hookah device 202 comprises a plurality ofmagnets 261 which enable the support plates 253-255 to be releasablyattached to one another. Once the hookah device 202 is assembled withthe support plates 253-255 and the PCBs 256-258 stacked on top of oneanother with the mist generator device 201 retained between the supportplates 253-255, the cover 250 is placed onto the base 249 and aplurality of screws 262 are used to releasably attach the cover 250 tothe base 249.

The upper support plate 253 comprises a manifold 263 which is positionedcentrally on one side of the upper support plate 253. In thisarrangement, the manifold 263 is provided with four apertures 264 (onlyone of which is visible in FIG. 56) which each receive the outlet port208 of a respective mist generator device 201. In this arrangement, thehookah device 202 comprises four mist generator devices 201 which arereleasably coupled to the manifold at 90° relative to one another. Inother arrangements, the manifold 263 comprises a different number ofapertures 264 to correspond with the number of mist generator devices201 being used with the hookah device 202.

The manifold 263 comprises a manifold pipe 265 which is in fluidcommunication with the apertures 264 such that mist generated by themist generator devices 201 can combine and flow down from the manifold263 and out of the manifold pipe 265. When the hookah device 202 isassembled, the manifold pipe 265 extends through an aperture 266 in themiddle support plate 254 and an aperture 267 in the middle PCB 257. Themanifold pipe 265 then connects to an outlet pipe 268 which extendsthrough the lower support plate 255 to provide a fluid flow path throughthe lower support plate to the hookah outlet port 252 of the hookahdevice 202.

In use, each of the mist generator devices 201 is held by the manifoldin a horizontal orientation. That is to say, the longitudinal length ofeach mist generator device 201 is perpendicular or generallyperpendicular to the direction of flow of mist as the mist flowsdownwardly from the base of the hookah device 202.

The outlet pipe 268 extends downwardly from the underside of the lowersupport plate 255 and through and aperture 269 in the lower PCB 258. Theoutlet pipe 268 then extends through an aperture 270 in the base 249 ofthe hookah device 202. In this arrangement, the outlet pipe 268 and thehookah outlet port 252 are a hookah attachment arrangement 271 whichattaches or is configured to attach the hookah device 202 to a hookah246. In this arrangement, the hookah device 202 is attached to thehookah 246 by inserting part of the stem 247 of the hookah into thehookah outlet port 252.

The hookah outlet port 252 provides a fluid flow path 272, as shown inFIGS. 58 and 59, from the mist outlet ports 208 of the mist generatordevices 201 and out of the hookah device 202 such that mist generated bythe mist generator devices 201 flows out from the hookah device 202 andinto the hookah 246. The mixture of air and mist creates bubbles in thewater of the hookah 246. The bubbles escape the water surface with themist rising above the surface of water in the water bowl of the hookahand travel through the pipe to the user during inhalation.

In this arrangement, the upper PCB 256 carries a pressure sensor whichsenses the pressure of air in the vicinity of the mist outlet ports 208of the mist generator devices 201. The pressure sensor thereby detects anegative pressure in the vicinity of the mist outlet ports 208 when auser draws on the hookah and sucks air through the mist generatordevices 201 along the fluid flow path 272. The pressure sensor providesa signal to the controller of the hookah device, as described below, forthe controller to activate at least one of the mist generator devices201 to generate mist as the user draws on the hookah.

In this arrangement, the lower PCB 258 carries power control components273 which control and distribute power to the other electroniccomponents of the hookah device 202. In some arrangements, the powercontrol components 273 receive power from an external power source, suchas a mains power adapter, which is releasably attached to the hookahdevice 202. In this arrangement, the hookah head 202 is configured to bepowered by an external power adaptor at a DC voltage in the range 20V to40V.

In other arrangements, the hookah device 202 comprises a battery whichis integrated within the hookah device 202 and connected to the powercontrol components 273. In some arrangements, the battery is arechargeable Li—Po battery. In some arrangements, the battery isconfigured to output a 20V to 40V DC voltage. In some arrangements, thebattery has a high discharge rate. The high discharge rate is necessaryfor the voltage amplification that is required by the ultrasonictransducers of the mist generator devices 201. Due to the requirement ofhaving a high discharge rate, the Li—Po battery of some arrangements isdesigned specifically for continuous current draw. In some arrangements,a charging port is provided on the hookah device 202 to enable thebattery to be charged by an external power source.

The middle PCB 257 incorporates a processor 274 and a memory 275 of acontroller or computing device of the hookah device 202. In thisexample, each PMIC 300 and each bridge IC 301 are mounted to the PCB 257along with the other electrical components of the hookah device 22. Inthis arrangement, the processor 274 and the memory 275 are components ofthe driver device within the hookah device 202. In this arrangement, thefunctionality of the driver device is implemented in executableinstructions which are stored in the memory 275 which, when executed bythe processor 274, cause the processor 274 to control the driver deviceto perform at least one function. The driver device is connectedelectrically to each of the mist generator devices 201. In thisarrangement, the driver device of the hookah device 202 is coupled forcommunication with each mist generator device 201 by a communicationsbus or data bus, such as an I²C data bus, as described above. In thisarrangement, each mist generator device 201 is identified by a uniqueidentifier which is used when controlling the mist generator device 201via the data bus (the microcontroller 303 controls each PMIC 300 via thedata bus which in turn controls the respective mist generator device201). In some arrangements, the unique identifier is stored in the OTPIC 242 of the mist generator device 201.

In some arrangements, the driver device (the microcontroller 303)controls each respective mist generator device independently. In somearrangements, the control functionality is implemented in executableinstructions stored in the memory 275. The independent controlconfiguration enables the driver device to activate or deactivate eachmist generator device 201 independently of the other mist generatordevices 201. The driver device can therefore control one or more of themist generator devices 201 to generate mist simultaneously oralternately according to predetermined requirements.

In some arrangements, the driver device controls the mist generatordevices 201 to activate and/or deactivate successively in sequence. Insome arrangements the sequence of activation of the mist generatordevices 201 optimizes the operation of the hookah device 202 by ensuringthat mist is generated sufficiently quickly to allow the mist to pass inbubbles through the water in the water chamber of the hookah. The hookahdevice 202 of some arrangements thereby enables bubbles of mist to bedrawn at high velocity through the water in the water chamber as a userdraws on the hookah mouthpiece. Consequently, water soluble compounds(e.g. vegetable glycerin, flavorings, etc.) are able to travel throughthe water in in the bubbles of mist for inhalation by a user.

In some arrangements, the driver device controls the mist generatordevices 201 to activate for a predetermined length of time one afteranother in sequence. In some arrangements, the driver device controlsthe mist generator devices 201 to activate in rotation such that themist generator devices 201 are activated one after the other and/or oneat a time in a clockwise or anticlockwise direction.

In some arrangements, the driver device controls the mist generatordevices 201 to activate in pairs. In some arrangements, the driverdevice controls two mist generator devices 201 to activatesimultaneously; either two mist generator devices 201 that are adjacentto one another or two mist generator devices that are opposite oneanother.

In some arrangements, the driver device is configured to ensure that amist generator device 201 is not activated if it is not properly wickedwith e-liquid in its capillary 222 or if the liquid chamber 218 empty ornearly empty of e-liquid. This provides protection for the hookah device202 by ensuring that the hookah device 202 maintains correct operation.

The electronics of the driver device of the hookah device 202(distributed across the PCBs 256-258) are divided as discussed below.The following description refers to the control of one mist generatordevice 201 but it is to be appreciated that the driver device of thehookah device 202 controls each mist generator device 201 independentlyin the same way.

In order to obtain the most efficient aerosolization, with particle sizebelow 1 um, the driver device provides the contacts pads receiving theultrasonic transducer 215 (piezoelectrical ceramic disc (PZT)) with highadaptive frequency (approximately 3 MHz).

This section not only has to provide high frequency but also protect theultrasonic transducer 215 against failures while providing constantoptimized cavitation.

PZT mechanical deformation is linked to the AC Voltage amplitude that isapplied to it, and in order to guarantee optimal functioning anddelivery of the system at every sonication, the maximum deformation mustbe supplied to the PZT all the time.

However, in order to prevent the failure of the PZT, the active powertransferred to it must be precisely controlled.

The processor 274 and the memory 275 are configured to controlmodulation of the active power given to the PZT at every instant withoutcompromising the mechanical amplitude of vibration of the PZT.

By Pulse Width Modulation (PWM) of the AC voltage applied to the PZT,the mechanical amplitude of the vibration remains the same.

Indeed, the RMS voltage applied would be the same with effective DutyCycle modulation as with Voltage modulation, but the active powertransferred to the PZT would degrade. Indeed, given the formula below:

Active Power displayed to the PZT being Pa=2√{square root over(2)}/πIrms*Vrms*cos φ,

Where

φ is the shift in phase between current and voltage

I_(rms) is the root mean square Current

V_(rms) is the root mean square Voltage.

When considering the first harmonic, Irms is a function of the realvoltage amplitude applied to the transducer, as the pulse widthmodulation alters the duration of voltage supplied to the transducer,controlling Irms.

The specific design of the PMIC uses a state-of-the-art design, enablingultra-precise control of the frequency range and steps to apply to thePZT including a complete set of feedback loops and monitoring path forthe control section to use.

In this arrangement, the driver device comprises a DC/DC boost converterand transformer that carry the necessary power to the PZT contact pads.

In this arrangement, the driver device comprises an AC driver forconverting a voltage from the battery into an AC drive signal at apredetermined frequency to drive the ultrasonic transducer.

The driver device comprises an active power monitoring arrangement formonitoring the active power used by the ultrasonic transducer (asdescribed above) when the ultrasonic transducer is driven by the ACdrive signal. The active power monitoring arrangement provides amonitoring signal which is indicative of an active power used by theultrasonic transducer.

The processor 274 within the driver device controls the AC driver andreceives the monitoring signal drive from the active power monitoringarrangement.

The memory 275 of driver device stores instructions which, when executedby the processor, cause the processor to:

-   -   A. control the AC driver to output an AC drive signal to the        ultrasonic transducer at a sweep frequency.    -   B. calculate the active power being used by the ultrasonic        transducer based on the monitoring signal;    -   C. control the AC driver to modulate the AC drive signal to        maximize the active power being used by the ultrasonic        transducer;    -   D. store a record in the memory of the maximum active power used        by the ultrasonic transducer and the sweep frequency of the AC        drive signal;    -   E. repeat steps A-D for a predetermined number of iterations        with the sweep frequency incrementing or decrementing with each        iteration such that, after the predetermined number of        iterations has occurred, the sweep frequency has been        incremented or decremented from a start sweep frequency to an        end sweep frequency;    -   F. identify from the records stored in the memory the optimum        frequency for the AC drive signal which is the sweep frequency        of the AC drive signal at which a maximum active power is used        by the ultrasonic transducer; and    -   G. control the AC driver to output an AC drive signal to the        ultrasonic transducer at the optimum frequency to drive the        ultrasonic transducer to atomize a liquid.

In some arrangements, the active power monitoring arrangement comprisesa current sensing arrangement for sensing a drive current of the ACdrive signal driving the ultrasonic transducer, wherein the active powermonitoring arrangement provides a monitoring signal which is indicativeof the sensed drive current.

In some arrangements, the current sensing arrangement comprises anAnalog-to-Digital Converter which converts the sensed drive current intoa digital signal for processing by the processor.

In some arrangements, the start frequency is 2900 kHz and the endfrequency is 3100 kHz. In other arrangements, the start frequency is3100 kHz and the end frequency is 2900 kHz.

In some arrangements, the memory stores instructions which, whenexecuted by the processor, cause the processor to: repeat steps A-Dabove with the sweep frequency being incremented from a start sweepfrequency of 2900 kHz to an end sweep frequency of 2960 kHz.

In some arrangements, the memory stores instructions which, whenexecuted by the processor, cause the processor to: repeat steps A-Dabove with the sweep frequency being incremented from a start sweepfrequency of 2900 kHz to an end sweep frequency of 3100 kHz.

In some arrangements, the memory stores instructions which, whenexecuted by the processor, cause the processor to: in step G, controlthe AC driver to output an AC drive signal to the ultrasonic transducerat frequency which is shifted by a predetermined shift amount from theoptimum frequency.

In some arrangements, the predetermined shift amount is between 1-10% ofthe optimum frequency.

The pressure sensor used in the device serves two purposes. The firstpurpose is to prevent unwanted and accidental start of the sonic engine(driving the ultrasonic transducer). This functionality is implementedin the processing arrangement of the device, but optimized for lowpower, to constantly measure environmental parameters such astemperature and ambient pressure with internal compensation andreference setting in order to accurately detect and categories what iscalled a true inhalation.

The second purpose of the pressure sensor is to be able to monitor notonly the exact duration of the inhalations by the user for preciseinhalation volume measurement, but also to be able to determine thestrength of the user inhalation. All in all, we are able to completelydraw the pressure profile of every inhalation and anticipate the end ofan inhalation for aerosolization optimization.

In some arrangements, the hookah device 202 comprises a Bluetooth™ LowEnergy (BLE) microcontroller. Indeed, this enables the setting toprovide extremely accurate inhalation times, optimized aerosolization,monitor numerous parameters to guarantee safe misting and prevent theuse of non-genuine e-liquids or aerosol chambers and protect both thedevice against over-heating risks and the user against over-misting inone shot.

The use of the BLE microcontroller allows over-the-air update tocontinuously provide improved software to users based on anonymized datacollection and trained AI for PZT modelling. The BLE microcontrolleralso enables a remote computing device to communicate with the hookahdevice 202 so that the remote computing device can control the operationof the hookah device 202. In one example, a plurality of hookah devicesare controlled by one or more remote computing devices, for instance ina hookah or shisha bar to enable the manager of the bar to control theoperation and/or monitor the state of each hookah device.

In one example, data indicative of the status of each mist generatordevice in each hookah device is transmitted by the hookah device to aremote computing device so that the remote computing device can monitorthe status of each individual mist generator device. This enables amanager or user to track when each mist generator device is low onliquid or not operating correctly, so that the mist generator device canbe replaced.

The hookah device 202 is a precise, reliable and a safe aerosolizationsolution for daily customer usage and, as such, must provide acontrolled and trusted aerosolization.

This is performed through an internal method that can be broken apartinto several sections as follows:

Sonication

In order to provide the most optimal aerosolization the ultrasonictransducer (PZT) or each mist generator device 201 needs to vibrate inthe most efficient way.

Frequency

The electromechanical properties of piezoelectrical ceramics state thatthe component has the most efficiency at the resonant frequency. Butalso, vibrating a PZT at resonance for a long duration will inevitablyend with the failure and breaking of the component which renders theaerosol chamber unusable.

Another important point to consider when using piezoelectrical materialsis the inherent variability during manufacturing and its variabilityover temperature and lifetime.

Resonating a PZT at 3 MHz in order to create droplets of a size <1 umrequires an adaptive method in order to locate and target the ‘sweetspot’ of the particular PZT inside every aerosol chamber used with thedevice for every single inhalation.

Sweep

Because the device has to locate the ‘sweet spot’ for every singleinhalation and because of over-usage, the PZT temperature varies as thedevice uses an in-house double sweep method.

The first sweep is used when the device has not been used with aparticular aerosol chamber for a time that is considered enough for allthe thermal dissipation to occur and for the PZT to cool down to‘default temperature’. This procedure is also called a cold start.During this procedure the PZT needs a boost in order to produce therequired aerosol. This is achieved by only going over a small subset ofFrequencies between 2900 kHz to 2960 kHz which, considering extensivestudies and experiments, covers the resonant point.

For each frequency in this range, the sonic engine in activated and thecurrent going through the PZT is actively monitored and stored by themicrocontroller via an Analog-to-Digital Converter (ADC), and convertedback to current in order to be able to precisely deduct the Power usedby the PZT.

This yields the cold profile of this PZT regarding frequency and theFrequency used throughout the inhalation is the one that uses the mostcurrent, meaning the lowest impedance Frequency.

The second sweep is performed during any subsequent inhalation and coverthe entire range of frequencies between 2900 kHz to 3100 kHz due to themodification of the PZT profile with regards to temperature anddeformation. This hot profile is used to determine the shift to apply.

Shift

Because the aerosolization must be optimal, the shift is not used duringany cold inhalation and the PZT will hence vibrate at resonantfrequency. This can only happen for a short and unrepeated duration oftime otherwise the PZT would inevitably break.

The shift however is used during most of inhalations as a way to stilltarget a low impedance frequency, thus resulting in quasi-optimaloperation of the PZT while protecting it against failures.

Because the hot and cold profiles are stored during inhalation themicrocontroller can then select the proper shifted frequency accordingto the measured values of current through the PZT during sweep andensure a safe mechanical operation.

The selection of the direction to shift is crucial as thepiezoelectrical component behaves in a different way if outside theduplet resonant/anti-resonant frequency or inside this range. Theselected shift should always be in this range defined by Resonant toanti-Resonant frequencies as the PZT is inductive and not capacitive.

Finally, the percentage to shift is maintained below 10% in order tostill remain close to the lowest impedance but far enough of theresonance.

Adjustment

Because of the intrinsic nature of PZTs, every inhalation is different.Numerous parameters other than the piezoelectrical element influence theoutcome of the inhalation, like the amount of e-liquid remaining insidethe aerosol chamber, the wicking state of the gauze or the battery levelof the device.

As of this, the device permanently monitors the current used by the PZTinside the aerosol chamber and the microcontroller constantly adjuststhe parameters such as the frequency and the Duty Cycle in order toprovide the aerosol chamber with the most stable power possible within apre-defined range that follows the studies and experimental results formost optimal safe aerosolization.

Battery Monitoring

In some arrangements, a battery is integrated within the hookah device202. In these arrangements, the hookah device 202 is powered by a DCLi—Po battery which provides a required voltage to the hookah device202. Due to the requirement of having a high discharge rate, the Li—Pobattery of some arrangement is designed specifically for continuouscurrent draw.

Because the battery voltage drops and varies a lot when activating thesonication section, the microcontroller constantly monitors the powerused by the PZT inside the aerosol chamber to ensure a proper but alsosafe aerosolization.

And because the key to aerosolization is control, the device ensuresfirst that the Control and Information section of the device alwaysfunction and does not stop in the detriment of the sonication section.

This is why the adjustment method also takes into great account the realtime battery level and, if need be, modifies the parameters like theDuty Cycle to maintain the battery at a safe level, and in the case of alow battery before starting the sonic engine, the Control andInformation section will prevent the activation.

Power Control

As being said, the key to aerosolization is control and the method usedin the device is a real time multi-dimensional function that takes intoaccount the profile of the PZT, the current inside the PZT and thebattery level of the device at all time.

All this is only achievable thanks to the use of a microcontroller thatcan monitor and control every element of the device to produce anoptimal inhalation.

Interval

Because the device relies on a piezoelectrical component, the deviceprevents the activation of the sonication section if an inhalationstops. The safety delay in between two inhalations is adaptive dependingon the duration of the previous one. This allows the gauze to wickproperly before the next activation.

With this functioning, the device can safely operate and theaerosolization is rendered more optimal with no risk of breaking the PZTelement nor exposing the user to toxic components.

Connectivity (BLE)

The device Control and Information section is composed of a wirelesscommunication system in the form of a Bluetooth Low Energy capablemicrocontroller. The wireless communication system is in communicationwith the processor of the device and is configured to transmit andreceive data between the driver device and a computing device, such as asmartphone.

The connectivity via Bluetooth Low Energy to a companion mobileapplication ensures that only small power for this communication isrequired thus allowing the device to remain functioning for a longerperiod of time if not used at all, compared to traditional wirelessconnectivity solutions like Wi-Fi, classic Bluetooth, GSM or even LTE-Mand NB-IOT.

Most importantly, this connectivity is what enables the OTP as a featureand the complete control and safety of the inhalations. Every data fromresonant frequency of an inhalation to the one used, or the negativepressure created by the user and the duration are stored and transferredover BLE for further analysis and improvements of the embedded software.

Finally, this connectivity enables the update of the embedded firmwareinside the device and over the air (OTA), which guarantees that thelatest versions can always be deployed rapidly. This gives greatscalability to the device and insurance that the device is intended tobe maintained.

In one example, the hookah device incorporates a mist inhaler device 200which comprises an active power monitor which incorporates a currentsensor, such as the current sensor 335 described above, for sensing anrms drive current of the AC drive signal driving the ultrasonictransducer 215. The active power monitor provides a monitoring signalwhich is indicative of the sensed drive current, as described above.

The additional functionality of this example enables the mist inhalerdevice 200 to monitor the operation of the ultrasonic transducer whilethe ultrasonic transducer is activated. The mist inhaler device 200calculates an effectiveness value or quality index which is indicativeof how effective the ultrasonic transducer is operating to atomise aliquid within the device. The device uses the effectiveness value tocalculate the actual amount of mist that was generated over the durationof activation of the ultrasonic transducer.

Once the actual amount of mist has been calculated, the device isconfigured to calculate the actual amount of a drug which was present inthe mist and hence the actual amount of a drug which was inhaled by auser based on the concentration of the drug in the liquid.

In practice, as described above, there are many different factors whichaffect the operation of an ultrasonic transducer and which have animpact on the amount of mist which is generated by the ultrasonictransducer and hence the actual amount of a drug which is delivered to auser.

The configuration of the mist inhaler device and a method of generatingmist using the mist inhaler device of some examples will now bedescribed in detail below.

In this example, the mist inhaler device incorporates the components ofthe mist inhaler device 200 described above, but the memory of thedriver device 202 further stores instructions which, when executed bythe processor, cause the processor to activate the mist generator device200 for a first predetermined length of time. As described above, themist generator device is activated by driving the ultrasonic transducer215 in the mist generator device 200 with the AC drive signal so thatthe ultrasonic transducer 215 atomises liquid carried by the capillaryelement 222.

The executed instructions cause the processor to sense, using a currentsensor, periodically during the first predetermined length of time thecurrent of the AC drive signal flowing through the ultrasonic transducer215 and storing periodically measured current values in the memory.

The executed instructions cause the processor to calculate aneffectiveness value using the current values stored in the memory. Theeffectiveness value is indicative of the effectiveness of the operationof the ultrasonic transducer at atomising the liquid.

In one example, the executed instructions cause the processor tocalculate the effectiveness value using this equation:

$Q_{l} = \frac{\sum_{t = 0}^{t = D}\frac{\sqrt{Q_{A(t)}^{2} + Q_{F(t)}^{2}}}{\sqrt{2}}}{N}$

where:

-   -   Q_(I) is the effectiveness value,    -   Q_(F) is a frequency sub-effectiveness value which is based on        the monitored frequency value (the frequency at which the        ultrasonic transducer 215 is being driven),    -   Q_(A) is an analogue to digital converter sub-effectiveness        value which is based on the measured current value (the rms        current flowing through the ultrasonic transducer 215),    -   t=0 is the start of the first predetermined length of time,    -   t=D is the end of the first predetermined length of time,    -   N is the number of periodic measurements (samples) during the        first predetermined length of time, and    -   √{square root over (2)} is a normalization factor.

In one example, the memory stores instructions which, when executed bythe processor, cause the processor to measure periodically during thefirst predetermined length of time the duty cycle of the AC drive signaldriving the ultrasonic transducer and storing periodically measured dutycycle values in the memory. The mist inhaler device then modifies theanalogue to digital converter sub-effectiveness value Q_(A) based on thecurrent values stored in the memory. Consequently, the mist inhalerdevice of this example takes into account variations in the duty cyclewhich may occur throughout the activation of the ultrasonic transducer215 when the device calculates the effectiveness value. The mist inhalerdevice can therefore calculate the actual amount of mist which isgenerated accurately by taking into account variations in the duty cycleof the AC drive signal which may occur while the ultrasonic transduceris activated.

The effectiveness value is used by the mist inhaler device as aweighting to calculate the actual amount of mist generated by the mistinhaler device by proportionally reducing a value of a maximum amount ofmist that would be generated if the device was operating optimally.

In one example, the memory stores instructions which, when executed bythe processor, cause the processor to measure periodically during thefirst predetermined length of time the frequency of the AC drive signaldriving the ultrasonic transducer 215 and storing periodically measuredfrequency values in the memory. The device then calculates theeffectiveness value using the using the frequency values stored in thememory, in addition to the current values as described above.

In one example, the memory stores instructions which, when executed bythe processor, cause the processor to calculate a maximum mist amountvalue that would be generated if the ultrasonic transducer 215 wasoperating optimally over the duration of the first predetermined lengthof time. In one example, the maximum mist amount value is calculatebased on modelling which determines the maximum amount of mist whichwould be generated when the ultrasonic transducer was operatingoptimally.

Once the maximum mist amount value has been calculated, the mist inhalerdevice can calculate an actual mist amount value by reducing the maximummist amount value proportionally based on the effectiveness value todetermine the actual mist amount that was generated over the duration ofthe first predetermined length of time.

Once the actual mist amount has been calculated, the mist inhaler devicecan calculate a drug amount value which is indicative of the amount of adrug in the actual mist amount that was generated over the duration ofthe first predetermined length of time. The mist inhaler device thenstores a record of the drug amount value in the memory.

In one example, the memory stores instructions which, when executed bythe processor, cause the processor to selecting a second predeterminedlength of time in response to the effectiveness value. In this case, thesecond predetermined length of time is a length of time over which theultrasonic transducer 215 is activated during a second inhalation orpuff by a user. In one example, the second predetermined length of timeis equal to the first predetermined length of time but with the timereduced or increased proportionally according to the effectivenessvalue. For instance, if the effectiveness value indicates that theultrasonic transducer 215 is not operating effectively, the secondpredetermined length of time is made longer by the effectiveness valuesuch that a desired amount of mist is generated during the secondpredetermined length of time.

When it comes to the next inhalation, the mist inhaler device activatesthe mist generator device for the second predetermined length of time sothat the mist generator device generates a predetermined amount of mistduring the second predetermined length of time. The mist inhaler devicethus controls the amount of mist generated during the secondpredetermined length of time accurately, taking into account the variousparameters which are reflected by the effectiveness value which affectthe operation of the mist inhaler device.

In one example, the memory stores instructions which, when executed bythe processor, cause the processor to activate the mist generator devicefor a plurality of predetermined lengths of time. For instance, the mistgenerator device is activated during a plurality of successiveinhalations or puffs by a user.

The mist inhaler device stores a plurality of drug amount values in thememory, each drug amount value being indicative of the amount of a drugin the mist that was generated over the duration of a respective one ofthe predetermined lengths of time.

The mist inhaler of some examples of this disclosure is configured totransmit data indicative of the drug amount values from the mistgenerator device to a computing device (e.g. via Bluetooth™ Low Energycommunication) for storage in a memory of the computing device (e.g. asmartphone). An executable application running on the computing devicecan thus log the amount of a drug which has been delivered to a user.The executable application can also control the operation of the mistinhaler device so that the application can modify the operation of eachmist inhaler device in the hookah device to accommodate for a mistinhaler device not operating in an optimal manner.

Because the aerosolization of the e-liquid is achieved via themechanical action of the piezoelectric disc and not due to the directheating of the liquid, the individual components of the e-liquid(propylene glycol, vegetable glycerin, flavoring components, etc.)remain largely in-tact and are not broken into smaller, harmfulcomponents such as acrolein, acetaldehyde, formaldehyde, etc. at thehigh rate seen in traditional ENDS.

All of the above applications involving ultrasonic technology canbenefit from the optimization achieved by the frequency controller whichoptimizes the frequency of sonication for optimal performance.

It is to be appreciated that the disclosures herein are not limited touse for nicotine delivery. The devices disclosed herein are for use withany drugs or other compounds (e.g. CBD), with the drug or compound beingprovided in a liquid within the liquid chamber of the device foraerosolization by the device.

The hookah device 202 of some arrangements is a healthier alternative toconventional hookah heads which burn tobacco using heat from charcoal oran electrical element. Nevertheless, the hookah device 202 of somearrangements still provides the same user experience as a conventionalhookah due to the mist bubbles in the water of the hookah. Users aretherefore likely to want to use the ultrasonic hookah device 202 of somearrangements instead of a conventional tobacco-burning hookah andthereby avoid the dangers of smoking tobacco in a hookah.

The foregoing outlines features of several arrangements, examples orembodiments so that those of ordinary skill in the art may betterunderstand various aspects of the present disclosure. Those of ordinaryskill in the art should appreciate that they may readily use the presentdisclosure as a basis for designing or modifying other processes andstructures for carrying out the same purposes and/or achieving the sameadvantages of various examples or embodiments introduced herein. Thoseof ordinary skill in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter of the appended claims is not necessarily limited tothe specific features or acts described above. Rather, the specificfeatures and acts described above are disclosed as example forms ofimplementing at least some of the claims.

Various operations of examples or embodiments are provided herein. Theorder in which some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated having the benefitof this description. Further, it will be understood that not alloperations are necessarily present in each embodiment provided herein.Also, it will be understood that not all operations are necessary insome examples or embodiments.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication and the appended claims are generally be construed to mean“one or more” unless specified otherwise or clear from context to bedirected to a singular form. Also, at least one of A and B and/or thelike generally means A or B or both A and B. Furthermore, to the extentthat “includes”, “having”, “has”, “with”, or variants thereof are used,such terms are intended to be inclusive in a manner similar to the term“comprising”. Also, unless specified otherwise, “first,” “second,” orthe like are not intended to imply a temporal aspect, a spatial aspect,an ordering, etc. Rather, such terms are merely used as identifiers,names, etc. for features, elements, items, etc. For example, a firstelement and a second element generally correspond to element A andelement B or two different or two identical elements or the sameelement.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others of ordinary skill in the art based upon a readingand understanding of this specification and the annexed drawings. Thedisclosure comprises all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described features(e.g., elements, resources, etc.), the terms used to describe suchfeatures are intended to correspond, unless otherwise indicated, to anyfeatures which performs the specified function of the described features(e.g., that is functionally equivalent), even though not structurallyequivalent to the disclosed structure. In addition, while a particularfeature of the disclosure may have been disclosed with respect to onlyone of several implementations, such feature may be combined with one ormore other features of the other implementations as may be desired andadvantageous for any given or particular application.

Examples or embodiments of the subject matter and the functionaloperations described herein can be implemented in digital electroniccircuitry, or in computer software, firmware, or hardware, including thestructures disclosed in this specification and their structuralequivalents, or in combinations of one or more of them.

Some examples or embodiments are implemented using one or more modulesof computer program instructions encoded on a computer-readable mediumfor execution by, or to control the operation of, a data processingapparatus. The computer-readable medium can be a manufactured product,such as hard drive in a computer system or an embedded system. Thecomputer-readable medium can be acquired separately and later encodedwith the one or more modules of computer program instructions, such asby delivery of the one or more modules of computer program instructionsover a wired or wireless network. The computer-readable medium can be amachine-readable storage device, a machine-readable storage substrate, amemory device, or a combination of one or more of them.

The terms “computing device” and “data processing apparatus” encompassall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus can include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, aruntime environment, or a combination of one or more of them. Inaddition, the apparatus can employ various different computing modelinfrastructures, such as web services, distributed computing and gridcomputing infrastructures.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output.

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto-optical disks, or optical disks. However, a computerneed not have such devices. Devices suitable for storing computerprogram instructions and data include all forms of non-volatile memory,media and memory devices.

In the present specification “comprise” means “includes or consists of”and “comprising” means “including or consisting of”.

The features disclosed in the foregoing description, or the followingclaims, or the accompanying drawings, expressed in their specific formsor in terms of a means for performing the disclosed function, or amethod or process for attaining the disclosed result, as appropriate,may, separately, or in any combination of such features, be utilized forrealizing the invention in diverse forms thereof.

Representative Features

Representative features are set out in the following clauses, whichstand alone or may be combined, in any combination, with one or morefeatures disclosed in the text and/or drawings of the specification.

1. A hookah device comprising:

-   -   a plurality of ultrasonic mist generator devices, wherein each        mist generator device incorporates:        -   a mist generator housing which is elongate and comprises an            air inlet port and a mist outlet port;        -   a liquid chamber provided within the mist generator housing,            the liquid chamber containing a liquid to be atomised;        -   a sonication chamber provided within the mist generator            housing;        -   a capillary element extending between the liquid chamber and            the sonication chamber such that a first portion of the            capillary element is within the liquid chamber and a second            portion of the capillary element is within the sonication            chamber;        -   an ultrasonic transducer having an atomisation surface,            wherein part of the second portion of the capillary element            is superimposed on part of the atomisation surface, and            wherein when the ultrasonic transducer is driven by an AC            drive signal the atomisation surface vibrates to atomise the            liquid carried by the second portion of the capillary            element to generate a mist comprising the atomised liquid            and air within the sonication chamber; and        -   an airflow arrangement which provides an air flow path            between the air inlet port, the sonication chamber and the            air outlet port, wherein the hookah device further            comprises:    -   a plurality of H-bridge circuits, wherein each H-bridge circuit        of the plurality of H-bridge circuits is connected to a        respective one of the ultrasonic transducers and generates an AC        drive signal to drive the ultrasonic transducer;    -   a microcontroller;    -   a data bus which is connected electrically to the        microcontroller to communicate data to and from the        microcontroller;    -   a plurality of microchips which are connected electrically to        the data bus to receive data from and transmit data to the        microcontroller, wherein each microchip of the plurality of        microchips is connected to a respective one of the H-bridge        circuits to control the H-bridge circuit to generate the AC        drive signal, wherein each microchip is a single unit which        comprises a plurality of interconnected embedded components and        subsystems comprising:    -   an oscillator which generates:        -   a main clock signal,        -   a first phase clock signal which is high for a first time            during the positive half-period of the main clock signal and            low during the negative half-period of the main clock            signal, and        -   a second phase clock signal which is high for a second time            during the negative half-period of the main clock signal and            low during the positive half-period of the main clock            signal, wherein the phases of the first phase clock signal            and the second phase clock signal are centre aligned;    -   a pulse width modulation (PWM) signal generator subsystem        comprising:        -   a delay locked loop which generates a double frequency clock            signal using the first phase clock signal and the second            phase clock signal, the double frequency clock signal being            double the frequency of the main clock signal, wherein the            delay locked loop controls the rising edge of the first            phase clock signal and the second phase clock signal to be            synchronous with the rising edge of the double frequency            clock signal, and wherein the delay locked loop adjusts the            frequency and the duty cycle of the first phase clock signal            and the second phase clock signal in response to a driver            control signal to produce a first phase output signal and a            second phase output signal, wherein the first phase output            signal and the second phase output signal are configured to            drive the H-bridge circuit connected to the microchip to            generate an AC drive signal to drive the ultrasonic            transducer;        -   a first phase output signal terminal which outputs the first            phase output signal to the H-bridge circuit connected to the            microchip;        -   a second phase output signal terminal which outputs the            second phase output signal to the H-bridge circuit connected            to the microchip;        -   a feedback input terminal which receives a feedback signal            from the H-bridge circuit, the feedback signal being            indicative of a parameter of the operation of the H-bridge            circuit connected to the microchip or AC drive signal when            the H-bridge circuit is driving the ultrasonic transducer            with the AC drive signal to atomise the liquid;    -   an analogue to digital converter (ADC) subsystem comprising:        -   a plurality of ADC input terminals which receive a plurality            of respective analogue signals, wherein one ADC input            terminal of the plurality of ADC input terminals is            connected to the feedback input terminal such that the ADC            subsystem receives the feedback signal from the H-bridge            circuit connected to the microchip, and wherein the ADC            subsystem samples analogue signals received at the plurality            of ADC input terminals at a sampling frequency which is            proportional to the frequency of the main clock signal and            the ADC subsystem generates ADC digital signals using the            sampled analogue signals;    -   a digital processor subsystem which receives the ADC digital        signals from the ADC subsystem and processes the ADC digital        signals to generate the driver control signal, wherein the        digital processor subsystem communicates the driver control        signal to the PWM signal generator subsystem to control the PWM        signal generator subsystem; and    -   a digital to analogue converter (DAC) subsystem comprising:        -   a digital to analogue converter (DAC) which converts a            digital control signal generated by the digital processor            subsystem into an analogue voltage control signal to control            a voltage regulator circuit which generates a voltage for            modulation by the H-bridge circuit connected to the            microchip; and        -   a DAC output terminal which outputs the analogue voltage            control signal to control the voltage regulator circuit to            generate a predetermined voltage for modulation by the            H-bridge circuit connected to the microchip to drive the            ultrasonic transducer in response to feedback signals which            are indicative of the operation of the ultrasonic            transducer; and    -   a hookah attachment arrangement which is configured to attach        the hookah device to a hookah, the hookah attachment arrangement        having a hookah outlet port which provides a fluid flow path        from the mist outlet ports of the mist generator devices and out        of the hookah device such that, when at least one of the mist        generator devices is activated by the driver device, mist        generated by each activated mist generator device flows along        the fluid flow path and out of the hookah device to the hookah.

2. The hookah device of clause 1, wherein the microcontroller isconfigured to identify and control each mist generator device using arespective unique identifier for the mist generator device.

3. The hookah device of clause 1, wherein each mist generator devicecomprises:

-   -   an identification arrangement comprising:        -   an integrated circuit having a memory which stores a unique            identifier for the mist generator device; and        -   an electrical connection which provides an electronic            interface for communication with the integrated circuit.

4. The hookah device of clause 1, wherein the microcontroller isconfigured to control each microchip and each respective mist generatordevice to activate independently of the other mist generator devices.

5. The hookah device of clause 4, wherein the microcontroller isconfigured to control the mist generator devices to activate in apredetermined sequence.

6. The hookah device of clause 1, wherein the hookah device comprises:

-   -   a manifold having a manifold pipe which is in fluid        communication with the mist outlet ports of the mist generator        devices, wherein mist output from the mist outlet ports combines        in the manifold pipe and flows through the manifold pipe and out        from the hookah device.

7. The hookah device of clause 6, wherein the hookah device comprisesfour mist generator devices which are releasably coupled to the manifoldat 90° relative to one another.

8. The hookah device of clause 1, wherein the feedback input terminalreceives a feedback signal from the H-bridge circuit in the form of avoltage which indicative of an rms current of an AC drive signal whichis driving the ultrasonic transducer.

9. The hookah device of clause 1, wherein each microchip furthercomprises:

-   -   a temperature sensor which is embedded within the microchip,        wherein the temperature sensor generates a temperature signal        which is indicative of the temperature of the microchip, and        wherein the temperature signal is received by a further ADC        input terminal of the ADC subsystem and the temperature signal        is sampled by the ADC.

10. The hookah device of clause 1, wherein the ADC subsystem samplessignals received at the plurality of ADC input terminals sequentiallywith each signal being sampled by the ADC subsystem a respectivepredetermined number of times.

11. The hookah device of clause 1, wherein the device further comprises:

-   -   a plurality of further microchips, wherein each further        microchip of the plurality of further microchips is connected to        a respective microchip of the plurality of microchips and        comprises one H-bridge circuit of the plurality of H-bridge        circuits, wherein each further microchip is a single unit which        comprises a plurality of interconnected embedded components and        subsystems comprising:        -   a first power supply terminal; and        -   a second power supply terminal, wherein        -   the H-bridge circuit in the further microchip incorporates a            first switch, a second switch, a third switch and a fourth            switch, and wherein:        -   the first switch and the third switch are connected in            series between the first power supply terminal and the            second power supply terminal;        -   a first output terminal is connected electrically between            the first switch and the third switch, wherein the first            output terminal is connected to a first terminal of the            ultrasonic transducer,        -   the second switch and the fourth switch are connected in            series between the first power supply terminal and the            second power supply terminal, and        -   a second output terminal is connected electrically between            the second switch and the fourth switch, wherein the second            output terminal is connected to a second terminal of the            ultrasonic transducer;        -   a first phase terminal which receives the first phase output            signal from the pulse width modulation (PWM) signal            generator subsystem;        -   a second phase terminal which receives a second phase output            signal from the PWM signal generator subsystem;        -   a digital state machine which generates timing signals based            on the first phase output signal and the second phase output            signal and outputs the timing signals to the switches of the            H-bridge circuit to control the switches to turn on and off            in a sequence such that the H-bridge circuit outputs an AC            drive signal for driving the ultrasonic transducer, wherein            the sequence comprises a free-float period in which the            first switch and the second switch are turned off and the            third switch and the fourth switch are turned on in order to            dissipate energy stored by the ultrasonic transducer;        -   a current sensor which incorporates:            -   a first current sense resistor which is connected in                series between the first switch and the first power                supply terminal;            -   a first voltage sensor which measures the voltage drop                across the first current sense resistor and provides a                first voltage output which is indicative of the current                flowing through the first current sense resistor;            -   a second current sense resistor which is connected in                series between the second switch and the first power                supply terminal;            -   a second voltage sensor which measures the voltage drop                across the second current sensor resistor and provides a                second voltage output which is indicative of the current                flowing through the second current sense resistor, and            -   a current sensor output terminal which provides an rms                output voltage relative to ground which is equivalent to                the first voltage output and the second voltage output,        -   wherein the rms output voltage is indicative of an rms            current flowing through the first switch or the second            switch and the current flowing through the ultrasonic            transducer which is connected between the first output            terminal and the second output terminal.

12. The hookah device of clause 11, wherein the H-bridge circuit in eachfurther microchip is configured to output a power of 22 W to 50 W to theultrasonic transducer which is connected to the first output terminaland the second output terminal.

13. The hookah device of clause 11, wherein each further microchipcomprises:

-   -   a temperature sensor which is embedded within the further        microchip, wherein the temperatures sensor measures the        temperature of the further microchip and disables at least part        of the further microchip in the event that the temperature        sensor senses that the further microchip is at a temperature        which is in excess of a predetermined threshold.

14. The hookah device of clause 11, wherein the device furthercomprises:

-   -   a boost converter circuit which is configured to increase a        power supply voltage to a boost voltage in response to the        analogue voltage output signal from the DAC output terminal,        wherein the boost converter circuit provides the boost voltage        at the first power supply terminal such that the boost voltage        is modulated by the switching of the switches of the H-bridge        circuit.

15. The hookah device of clause 11, wherein the current sensor sensesthe current flowing through the resonant circuit during the free-floatperiod and the digital state machine adapts the timing signals to switchon either the first switch or the second switch when the current sensorsenses that the current flowing through the resonant circuit during thefree-float period is zero.

16. The hookah device of clause 11, wherein, during a setup phase ofoperation of the device, the further microchip:

-   -   measures the length of time taken for the current flowing        through the resonant circuit to fall to zero when the first        switch and the second switch are turned off and the third switch        and the fourth switch are turned on; and    -   sets the length of time of the free-float period to be equal to        the measured length of time.

17. The hookah device of clause 1, wherein the device further comprises:

-   -   a memory storing instructions which, when executed by the        microcontroller, cause the microchip to:        -   A. control the H-bridge circuit to output an AC drive signal            to the ultrasonic transducer at a sweep frequency;        -   B. calculate the active power being used by the ultrasonic            transducer based on the feedback signal;        -   C. control the H-bridge circuit to modulate the AC drive            signal to maximise the active power being used by the            ultrasonic transducer;        -   D. store a record in the memory of the maximum active power            used by the ultrasonic transducer and the sweep frequency of            the AC drive signal;        -   E. repeat steps A-D for a predetermined number of iterations            with the sweep frequency incrementing or decrementing with            each iteration such that, after the predetermined number of            iterations has occurred, the sweep frequency has been            incremented or decremented from a start sweep frequency to            an end sweep frequency;        -   F. identify from the records stored in the memory the            optimum frequency for the AC drive signal which is the sweep            frequency of the AC drive signal at which a maximum active            power is used by the ultrasonic transducer; and        -   G. control the H-bridge circuit to output an AC drive signal            to the ultrasonic transducer at the optimum frequency to            drive the ultrasonic transducer to atomise a liquid.

18. The hookah device of clause 17, wherein the start sweep frequency is2900 kHz and the end sweep frequency is 3100 kHz.

19. A hookah comprising:

-   -   a water chamber;    -   an elongate stem having a first end which is attached to the        water chamber, the stem comprising a mist flow path which        extends from a second end of the stem, through the stem, to the        first end; and    -   a hookah device comprising:        -   a plurality of ultrasonic mist generator devices, wherein            each mist generator device incorporates:            -   a mist generator housing which is elongate and comprises                an air inlet port and a mist outlet port;            -   a liquid chamber provided within the mist generator                housing, the liquid chamber containing a liquid to be                atomised;            -   a sonication chamber provided within the mist generator                housing;            -   a capillary element extending between the liquid chamber                and the sonication chamber such that a first portion of                the capillary element is within the liquid chamber and a                second portion of the capillary element is within the                sonication chamber;            -   an ultrasonic transducer having an atomisation surface,                wherein part of the second portion of the capillary                element is superimposed on part of the atomisation                surface, and wherein when the ultrasonic transducer is                driven by an AC drive signal the atomisation surface                vibrates to atomise the liquid carried by the second                portion of the capillary element to generate a mist                comprising the atomised liquid and air within the                sonication chamber; and            -   an airflow arrangement which provides an air flow path                between the air inlet port, the sonication chamber and                the air outlet port, wherein the hookah device further                comprises:        -   a plurality of H-bridge circuits, wherein each H-bridge            circuit of the plurality of H-bridge circuits connects to a            respective one of the ultrasonic transducers, wherein the            H-bridge circuit generates an AC drive signal to drive the            ultrasonic transducer;        -   a microcontroller;        -   a data bus which is connected electrically to the            microcontroller to communicate data to and from the            microcontroller;        -   a plurality of microchips which are connected electrically            to the data bus to receive data from and transmit data to            the microcontroller, wherein each microchip of the plurality            of microchips connects connected to a respective one of the            H-bridge circuits to control the H-bridge circuit to            generate the AC drive signal, wherein each microchip is a            single unit which comprises a plurality of interconnected            embedded components and subsystems comprising:        -   an oscillator which generates:            -   a main clock signal,            -   a first phase clock signal which is high for a first                time during the positive half-period of the main clock                signal and low during the negative half-period of the                main clock signal, and            -   a second phase clock signal which is high for a second                time during the negative half-period of the main clock                signal and low during the positive half-period of the                main clock signal, wherein the phases of the first phase                clock signal and the second phase clock signal are                centre aligned;            -   a pulse width modulation (PWM) signal generator                subsystem comprising:            -   a delay locked loop which generates a double frequency                clock signal using the first phase clock signal and the                second phase clock signal, the double frequency clock                signal being double the frequency of the main clock                signal, wherein the delay locked loop controls the                rising edge of the first phase clock signal and the                second phase clock signal to be synchronous with the                rising edge of the double frequency clock signal, and                wherein the delay locked loop adjusts the frequency and                the duty cycle of the first phase clock signal and the                second phase clock signal in response to a driver                control signal to produce a first phase output signal                and a second phase output signal, wherein the first                phase output signal and the second phase output signal                are configured to drive the H-bridge circuit connected                to the microchip to generate an AC drive signal to drive                the ultrasonic transducer; a first phase output signal                terminal which outputs the first phase output signal to                the H-bridge circuit connected to the microchip;            -   a second phase output signal terminal which outputs the                second phase output signal to the H-bridge circuit                connected to the microchip;            -   a feedback input terminal which receives a feedback                signal from the H-bridge circuit, the feedback signal                being indicative of a parameter of the operation of the                H-bridge circuit connected to the microchip or AC drive                signal when the H-bridge circuit is driving the                ultrasonic transducer with the AC drive signal to                atomise the liquid;        -   an analogue to digital converter (ADC) subsystem comprising:            -   a plurality of ADC input terminals which receive a                plurality of respective analogue signals, wherein one                ADC input terminal of the plurality of ADC input                terminals is connected to the feedback input terminal                such that the ADC subsystem receives the feedback signal                from the H-bridge circuit connected to the microchip,                and wherein the ADC subsystem samples analogue signals                received at the plurality of ADC input terminals at a                sampling frequency which is proportional to the                frequency of the main clock signal and the ADC subsystem                generates ADC digital signals using the sampled analogue                signals;        -   a digital processor subsystem which receives the ADC digital            signals from the ADC subsystem and processes the ADC digital            signals to generate the driver control signal, wherein the            digital processor subsystem communicates the driver control            signal to the PWM signal generator subsystem to control the            PWM signal generator subsystem; and        -   a digital to analogue converter (DAC) subsystem comprising:            -   a digital to analogue converter (DAC) which converts a                digital control signal generated by the digital                processor subsystem into an analogue voltage control                signal to control a voltage regulator circuit which                generates a voltage for modulation by the H-bridge                circuit connected to the microchip; and            -   a DAC output terminal which outputs the analogue voltage                control signal to control the voltage regulator circuit                to generate a predetermined voltage for modulation by                the H-bridge circuit connected to the microchip to drive                the ultrasonic transducer in response to feedback                signals which are indicative of the operation of the                ultrasonic transducer; and

a hookah attachment arrangement which is attached to the stem of thehookah at the second end of the stem, the hookah attachment arrangementhaving a hookah outlet port which provides a fluid flow path from themist outlet ports of the mist generator devices and out of the hookahdevice such that, when at least one of the mist generator devices isactivated by the driver device, mist generated by each activated mistgenerator device flows along the fluid flow path and out of the hookahdevice to the hookah.

Although certain example embodiments of the invention have beendescribed, the scope of the appended claims is not intended to belimited solely to these embodiments. The claims are to be construedliterally, purposively, and/or to encompass equivalents.

1. A hookah device for use with a hookah having an elongate stem and awater chamber with a first end of the stem attached to the waterchamber, the hookah device comprising: a manifold having a manifold pipeand a plurality of apertures, wherein each aperture of the plurality ofapertures is in fluid communication with the manifold pipe and isconfigured to receive a mist outlet port of a respective ultrasonic mistgenerator device, wherein each aperture of the plurality of apertures isformed in a respective side wall of the manifold and the manifold pipeis provided on an end wall of the manifold; a driver device which isconfigured to connect electrically to each of the mist generator devicesand configured to activate the mist generator devices; and a hookahattachment arrangement which is configured to attach the hookah deviceto a second end of the stem of the hookah, the hookah attachmentarrangement having a hookah outlet port which is in fluid communicationwith the manifold pipe and provides a fluid flow path out of the hookahdevice such that, when at least one of the mist generator devices isactivated by the driver device, mist generated by each activated mistgenerator device combines in the manifold and flows through the manifoldpipe and the hookah outlet port and out of the hookah device to thehookah.
 2. The hookah device of claim 1, wherein the end wall of themanifold is perpendicular to each side wall.
 3. The hookah device ofclaim 1, wherein the hookah device is configured to receive four mistgenerator devices which are releasably coupled to the manifold at 90°relative to one another.
 4. The hookah device of claim 1, wherein thehookah device further comprises a plurality of mist generator devices,wherein the plurality of mist generator devices are releasably coupledto the manifold.
 5. The hookah device of claim 4, wherein each mistgenerator device comprises: a mist generator housing which is elongateand comprises an air inlet port and the said mist outlet port; a liquidchamber provided within the mist generator housing, the liquid chambercontaining a liquid to be atomized; a sonication chamber provided withinthe mist generator housing; a capillary element extending between theliquid chamber and the sonication chamber such that a first portion ofthe capillary element is within the liquid chamber and a second portionof the capillary element is within the sonication chamber; an ultrasonictransducer having a generally planar atomization surface which isprovided within the sonication chamber, the ultrasonic transducer beingmounted within the mist generator housing such that the plane of theatomization surface is substantially parallel with a longitudinal lengthof the mist generator housing, wherein part of the second portion of thecapillary element is superimposed on part of the atomization surface,and wherein the ultrasonic transducer is configured to vibrate theatomization surface to atomize a liquid carried by the second portion ofthe capillary element to generate a mist comprising the atomized liquidand air within the sonication chamber; and an airflow arrangement whichprovides an air flow path between the air inlet port, the sonicationchamber and the air outlet port.
 6. The hookah device of claim 5,wherein each mist generator device further comprises: a transducerholder which is held within the mist generator housing, wherein thetransducer element holds the ultrasonic transducer and retains thesecond portion of the capillary element superimposed on part of theatomization surface; and a divider portion which provides a barrierbetween the liquid chamber and the sonication chamber, wherein thedivider portion comprises a capillary aperture through which part of thefirst portion of the capillary element extends.
 7. The hookah device ofclaim 5, wherein the capillary element is 100% bamboo fiber.
 8. Thehookah device of claim 5, wherein the airflow arrangement is configuredto change the direction of a flow of air along the air flow path suchthat the flow of air is substantially perpendicular to the atomizationsurface of the ultrasonic transducer as the flow of air passes into thesonication chamber.
 9. The hookah device of claim 5, wherein the liquidchamber contains a liquid having a kinematic viscosity between 1.05 Pa·sand 1.412 Pa·s and a liquid density between 1.1 g/ml and 1.3 g/ml. 10.The hookah device of claim 5, wherein the liquid chamber contains aliquid comprising approximately a 2:1 molar ratio of levulinic acid tonicotine.
 11. The hookah device of claim 1, wherein the driver devicecomprises: an AC driver which is configured to generate an AC drivesignal at a predetermined frequency to drive a respective ultrasonictransducer in each mist generator device; an active power monitoringarrangement which is configured to monitor the active power used by theultrasonic transducer when the ultrasonic transducer is driven by the ACdrive signal, wherein the active power monitoring arrangement isconfigured to provide a monitoring signal which is indicative of anactive power used by the ultrasonic transducer; a processor which isconfigured to control the AC driver and to receive the monitoring signaldrive from the active power monitoring arrangement; and a memory storinginstructions which, when executed by the processor, cause the processorto: A. control the AC driver to output an AC drive signal to theultrasonic transducer at a predetermined sweep frequency; B. calculatethe active power being used by the ultrasonic transducer based on themonitoring signal; C. control the AC driver to modulate the AC drivesignal to maximize the active power being used by the ultrasonictransducer; D. store a record in the memory of the maximum active powerused by the ultrasonic transducer and the sweep frequency of the ACdrive signal; E. repeat steps A-D for a predetermined number ofiterations with the sweep frequency incrementing with each iterationsuch that, after the predetermined number of iterations has occurred,the sweep frequency has been incremented from a start sweep frequency toan end sweep frequency; F. identify from the records stored in thememory the optimum frequency for the AC drive signal which is the sweepfrequency of the AC drive signal at which a maximum active power is usedby the ultrasonic transducer; and G. control the AC driver to output anAC drive signal to the ultrasonic transducer at the optimum frequency todrive the ultrasonic transducer to atomize a liquid.
 12. The hookahdevice of claim 11, wherein the active power monitoring arrangementcomprises: a current sensing arrangement which is configured to sense adrive current of the AC drive signal driving the ultrasonic transducer,wherein the active power monitoring arrangement is configured to providea monitoring signal which is indicative of the sensed drive current. 13.The hookah device of claim 11, wherein the memory stores instructionswhich, when executed by the processor, cause the processor to: repeatsteps A-D with the sweep frequency being incremented from a start sweepfrequency of 2900 kHz to an end sweep frequency of 2960 kHz.
 14. Thehookah device of claim 10, wherein the memory stores instructions which,when executed by the processor, cause the processor to: repeat steps A-Dwith the sweep frequency being incremented from a start sweep frequencyof 2900 kHz to an end sweep frequency of 3100 kHz.
 15. The hookah deviceof claim 11, wherein the AC driver is configured to modulate the ACdrive signal by pulse width modulation to maximize the active powerbeing used by the ultrasonic transducer.
 16. A hookah comprising: awater chamber; an elongate stem having a first end which is attached tothe water chamber, the stem comprising a mist flow path which extendsfrom a second end of the stem, through the stem, to the first end; and ahookah device, wherein the hookah attachment arrangement of the hookahdevice is attached to the stem of the hookah at the second end of thestem, the hookah device comprising: a manifold having a manifold pipeand a plurality of apertures, wherein each aperture of the plurality ofapertures is in fluid communication with the manifold pipe and isconfigured to receive a mist outlet port of a respective ultrasonic mistgenerator device, wherein each aperture of the plurality of apertures isformed in a respective side wall of the manifold and the manifold pipeis provided on an end wall of the manifold; a driver device which isconfigured to connect electrically to each of the mist generator devicesand configured to activate the mist generator devices; and a hookahattachment arrangement which is configured to attach the hookah deviceto a second end of the stem of the hookah, the hookah attachmentarrangement having a hookah outlet port which is in fluid communicationwith the manifold pipe and provides a fluid flow path out of the hookahdevice such that, when at least one of the mist generator devices isactivated by the driver device, mist generated by each activated mistgenerator device combines in the manifold and flows through the manifoldpipe and the hookah outlet port and out of the hookah device to thehookah.